What Lurks Beneath: Defeating a Stealthy Enemy - Lessons from the Battle of the Atlantic

This article was originally published in the Small Wars Journal

Abstract

An inferior, or "asymmetric", adversary often uses an area-denial approach against a superior force. This allows them to maintain a strategy of attrition against the stronger side's civilian homefront, while preserving their own force through stealth tactics. This research is not focused on IDF warfare in Lebanon or Gaza – it deals with the Battle of the Atlantic in World War II. The campaign began with the resounding failure by the Allies to learn lessons from the previous war, resulting in a strategic crisis. As the war progressed, a new type of response was developed – a force whose power was based not on the size of the ship or its cannons but in the range of its deployment, and principally on the combination of sensors, aerial surveillance, data processing and sensor-linked weapons. The WWII struggle at sea contains important lessons for land warfare today.

Introduction

For several decades, Western militaries have confronted a stubborn operational challenge. Our ability to bring our material superiority to bear in combat is hampered by our enemies' ability to hide and effectively disappear from the battlefield. At the same time, Western militaries continue to find ourselves exposed on the battlefield, vulnerable to attack.  How can we win against an enemy that we can't see?

The aim of this study is to draw lessons from Allied anti-submarine warfare in World War Two's Battle of the Atlantic for contemporary operational challenges against stealth enemies. The Battle of the Atlantic is the name given to the naval struggle between Germany and the Allies in which Germany attempted to blockade the British Isles through submarine attacks on Atlantic supply routes. The Germans sought to win in a war of attrition that rested on stealth area-denial tactics based on low-signature platforms that blended in with the maritime environment.

In order to extract insights from the Battle of the Atlantic as a relevant historical analogy, this study is divided into four short sections. The first deals with the operational learning conducted by the British in the interwar period. The second surveys the struggle in the Atlantic between the British and the Germans. The third section deals with Allied innovations in anti-submarine warfare. The fourth and last section examines the lessons that we can learn today from the historical case study, specifically the implications for contemporary force design against low-signature adversaries.

1.Learning, forgetting, and starting over

" Virtually every surface and air anti-submarine lesson of the first submarine war had to be, and ultimately was, re-learnt in the second at immense cost in blood, tears and treasure." - Lieutenant Commander D.W. Water, Royal Navy[1]

World War II was not the first time the British encountered German submarine warfare. Facing a disadvantage in surface ships, the Germany navy chose to employ this revolutionary form of warfare in World War I, starting in 1915. The submarine war was not on the margins of the war, but was instead a dramatic struggle that saw 2,600 Allied ships sent to the ocean floor. German successes even led to food rationing in Britain, including among its troops on the Western Front.[2] A significant portion of the operational wisdom that the British navy would eventually acquire in WWII had already been learned a generation earlier, then forgotten. Or, more accurately, it was repressed.[3] When the war ended in 1918, the convoy system was already in place, its importance recognized, and the first underwater sensors - hydrophones and sonar – had been developed. What's more, in WWI the British were already using SIGINT from cracking German codes and ELINT on submarine transmissions to locate the German U-boats. This intelligence allowed the British to hunt the submarines and to avoid ambushes altogether.[4]

Another important development during WWI was the development of naval aviation. Although they didn’t score many U-boat kills, shore-launched long-range aerial platforms and light planes launched from specially-outfitted ships proved their effectiveness in locating submarines and damaged a range of naval targets.

WWI provided a blueprint of what could be expected in a future war. Despite this, during the interwar period the world's leading navies continued to rely on the traditional measure of naval strength – surface fleets. This concept, which had already proved outdated in the First World War, manifested itself in the ongoing construction of cruisers and battleships. Submarines and aircraft carriers, which all the leading navies developed,[5] were still considered secondary supporting platforms in the British navy.[6]

In WWII, the Germans captured Norway and France in the spring of 1940, giving them convenient ports from which to access the Atlantic Ocean. The way was now open for the German U-boats to once again try to starve out the British through unlimited submarine warfare. The stamina of the British rested entirely on the maritime convoys in the Atlantic. Two-thirds of its food, 30% of its iron ore, 80% of its wood and its wool, 90% of its copper and its bauxite, 95% of its oil and 100% of its rubber, chromium and armaments imported from the US, all arrived by sea.

The British and Commonwealth navies, and later the US, would have to re-learn the lessons of the previous war, and to continue developing their anti-submarine doctrine. 

2.The Atlantic Campaign

"The only thing that really frightened me during the war was the U-Boat peril…I was even more anxious about this battle than I had been about the glorious air fight called The Battle of Britain." – Sir Winston Churchill[7]

Thirty thousand Allied sailors and merchant mariners were lost between September 1939 and May 1945. Their chances of survival were about 1 in 4. In total, 2,603 merchant ships and 175 warships were sunk, [8] and at the height of German successes the Allies lost 800,000  tons of shipping in a single month. [9] The loss of raw materials and armaments threatened the ability of the Americans and British to support the Soviet war effort, and to build enough military strength to invade Nazi-occupied Europe. In total, 1,156 U-boats participated in the campaign, including 400 at its height. The Germans lost 784 submarines, almost always with their crew. [10] Being a submariner on a U-boat, which were manned entirely by volunteers, was one of the most dangerous jobs in the war. Between 28,000-41,000 crewmen sunk to their watery graves, two-thirds of them in the Atlantic. [11]

The German surface fleet was not a worthy competitor to the British. It was instead the submarine fleet that quickly proved itself, due in large part to the new bases on the French coast that gave it a greater ability to strike British shipping. The diesel-electric submarines of WWII were in effect small surface ships with low silhouettes, armed with tube-launched torpedoes and a small cannon. These ships could dive underwater ahead of an encounter with an enemy, but most of the sailing was done on the surface. Its speed and the time it could spend underwater were limited by its electric batteries, which were charged when the air-consuming diesel engines operated on the surface. Most of the U-boats (Type VII) could sail at 17 knots on the surface (faster than merchant ships but slower than most destroyers), and 3-5 knots, or 5.5 km/h, while submerged.  Admiral Karl Doenitz, commander of the U-boat fleet, calculated that a force of 300 submarines, with 100 on patrols in the sea, would be enough to bring British shipping to starvation levels. [12] In February 1941, this strategy was formalized in Fuhrer's Directive no. 23.[13]

The German campaign was managed by Doenitz's submarine branch, which established its base in occupied France. The nature of submarine warfare and the fact that it primarily took place in the open sea, far from British air cover, meant that despite some coastal Luftwaffe operations, the German effort against Allied shipping relied mostly on submarine-only operations, without the participation of other services.

A U-boat shells a merchant ship that has remained afloat after being torpedoed. (IWM Photo No.: MISC 51237, public domain)

The British navy was responsible for protecting British shipping. It did this through a number of regional commands, the most important for this study being the Western Approaches Command, which was based in Liverpool and also directed the efforts of the Royal Canadian Navy.[14] Another important body was the Coastal Command, an aerial force that belonged to the Royal Air Force (RAF), whose original purpose was to combat a German amphibious invasion. The command was also seen as the "Cinderella" of the RAF, and suffered from a lack of long-range aircraft to fulfill its missions over the Atlantic. [15]

Despite the fact that the convoy escort system had already proved itself in World War I, the British Admiralty chose to focus on its offensive effort, in the long-established spirit of the Royal Navy.[16] The failure of its submarine hunting efforts in the Atlantic forced the Royal Navy to reorganize its convoy escort system. A major deficit in escort ships immediately became the limiting factor in this strategy. Building a force of escort ships- though small, slow, and lightly armed - became the urgent priority. The British bought outdated American destroyers and began building new classes of ships for the Royal Navy, like corvettes, the military version of whaling ships whose primary advantage was the ease with which they were built by civilian shipyards. [17]  After America's entrance into the war, upon the insistence of the US Navy, the Tenth Fleet was established with the mission of convoy escort anti-submarine warfare in the Atlantic Ocean. [18]

The consolidation of shipping by the British into convoys escorted by armed warships dramatically limited the effectiveness of lone submarines. In response, the Germans adopted the "wolfpack" tactic. [19] A U-boat screen was spread across the Atlantic, and when one of its number identified and reported a convoy, the submarines coordinated by encrypted high frequency radio signals through Doenitz's headquarters. A large force of U-boats was concentrated on the convoy's path and began its attack. In October 1940, for example, 8 U-boats attacked three separate convoys (SC7, HX-79, and HX-79A) sinking 38 merchantmen. [20]   

A bold U-boat tactic was to penetrate the convoy by sailing on the surface under the cover of night against the silhouettes of the larger ships, then to sink ships from within the British force. This allowed the submarines to sail at the speed of the convoy while avoiding detection by sonar.

The U-boat campaign enjoyed two peak periods, later called the "First Happy Time" (June 1940-December 1941) and the "Second Happy Time" (Operation Drumbeat off the shores of the US in early 1942). During the Happy Times U-boats could sink multiple ships on every Atlantic patrol. The main reason for the U-boats' success was Allied unpreparedness. Many of the ships sunk in the Second Happy Time were attacked while they sailed just off the illuminated shores of the United States without any escort, ignoring the operational lessons that had already emerged in that period. [21] At its height in November 1942, the rate of ships sunk matched that of new ships being produced in the shipyards of America, Canada, and the UK combined[22]  – more than 800,000 tons (over 200 ships) a month. [23] The critical moment in the campaign came in April-May 1943. The German submarine force was at its peak, with more than 120 U-boats at sea and 400 other vessels in port, and the rate of Allied shipping losses almost matched the November 1942 peak.

A submarine's main advantage was its ability to initiate an encounter. This didn’t come from especially impressive firepower. The Type VII U-boat carried a total of 22 torpedoes, a light deck gun, and an anti-aircraft gun. [24] It took several long minutes to reload its 4 forward torpedo tubes, and when it wasn’t diving it was undoubtedly the most lightly armed ship on the surface. Like a sniper in a land battle, the submarine could remain hidden until it took the shot, and then break contact after it was discovered. The key to defeating the submarine then was taking away its advantage - its stealth.

Airplanes proved themselves to be the main foe of the U-boats, as successful submarine hunting hinged on finding them. U-boats dove only in the face of an enemy. It was possible to locate them while they sailed on the surface. But it was extremely difficult for lookouts on ships to find them, as the U-boats submerged before contact. On the other hand, scout planes could fly at high altitudes, cover large areas, find the white wake of the submarine and approach it before being seen by the U-boat's lookouts. Beyond the ability to attack it immediately, identifying the submarine had two main implications. First, it forced it to submerge, which limited its mobility for a significant period of time. Second, the Royal Navy's war room received the location of the submarine. A complete situational assessment was created there, and convoys sailed around the lanes that the U-boats threatened. Without a significant force of planes launched from aircraft carriers until late in the war, the critical mission of air patrols relied on Coastal Command. [25] But this RAF command was more focused on preventing a German invasion of the island than protecting the long convoy lanes. Very few of the 300 planes in the command at the outset of the war were patrol planes with relevant ranges for this mission. [26]

Beyond the lookouts by patrol planes and ships, the British had two other major sources of intelligence. The first was Electronic Intelligence (ELINT) based location capabilities, called HF/DF (High Frequency Direction Finding). Since submarine warfare depended on centralized operational management by radio, the British developed a series of coastal stations across the globe whose role was to pinpoint the broadcasts and locate the submarine through triangulation. [27] Locating submarines through this method was not accurate enough to allow for effective hunting, but by the mid-1940s it did enable the allies to reroute convoys away from ambushes. Wolfpack tactics were largely designed to deal with this challenge by spreading a U-boat screen and converging on convoys that had been identified. The catch was that this dramatically increased their reliance on radio communications. [28]

The second and a more well-known intelligence development was the cracking of the German Enigma code. This Allied success allowed them to decipher the messages that U-boats sent to the central command room, including their precise locations. Still, the first cracking of the code only came in late 1941, and even then, it wasn’t always possible to decipher the message quickly enough for it to yield operational results. In the summer of 1942 the Enigma code was improved, and until the British managed to crack it again in early 1943 the U-boats were enjoying their Second Happy Time. As mentioned above, in April-May 1943 the U-boats in the Atlantic reached their peak strength, and Allied losses jumped sharply.  But this also represented the beginning of the end for the wolfpacks in the main shipping lanes.

3.The Smart Sensor Complex and the Allied anti-submarine revolution 1940-1945

The battle around Convoy ONS-5 (April 29- May 6)[29] reflects the turning point in the fight against the U-boats better than perhaps any other in the war. A force of 43 U-boats converged on a convoy, but managed to sink only 12 ships, at the price of 6 U-boats lost and 7 severely damaged. Over the course of that month 41 U-boats were sent to the bottom by British and American escorts. In less than a month the "Aces" – the top U-boat commanders – and almost all the veteran crews were lost, and in total the Germans lost almost half their operational force. Because of the serious blow he had suffered, Doenitz was forced to temporarily withdraw his forces from the ocean.[30] 

The dramatic change between the results of convoy battles in October 1940 and those in May 1943 happened because of a revolution in anti-submarine warfare. This development rested on a combination of advanced sensor technologies, new doctrine, and a reorganization of the anti-submarine system on both the tactical and operational levels.

What characterized this revolution? The Battle for the Atlantic was decided by a modern complex of sensors, advanced information processing and weapons designed to operate with the sensors. By 1945 the British had hundreds of escort ships, far inferior in terms of speed and firepower, but rich in a range of sensors – sonar, radar, and electronic sensors.

As important as it was, the intelligence campaign itself couldn’t be translated into operational success against the submarines. The British needed a sophisticated complex of sensors on the battlefield itself. Translating this complex into operational and tactical success was possible because of the ability to concentrate and process information, whether in a central war room or at sea by the escort commanders. This command and control system depended on communications capability (high frequency radio) and rapid learning mechanisms that could translate operational anomalies into tactical insights in real time. In the end, the daunting cannons of the British warships were replaced with a series of simple devices for dropping mines and depth charges. The main quality of these mechanisms was the ability to operate them in coordination with anti-submarine sensors on planes or ships.

There were four types of sensors that set the course of the information battle in the Atlantic – observation, acoustics, radio direction finding (radiogoniometry), and radar. All four used two complementary systems. The first was Line of Sight sensing, sensing in the proximity of the convoy. The second system was Non-Line of Sight sensing, further away from the convoy. Initially, the distant sensing was done by shore-based observation aircraft, and afterward by dozens of escort carriers, which were part of the escort and the U-boat hunting force. This system created a broad swath of wide area monitoring in the sea, which made the U-boats efforts to approach the convoys far more difficult.

In 1939 the Royal Navy had 180 ships, mostly destroyers, equipped with active acoustic sensors (ASDIC sonars). This was the only submarine-locating sensor the Royal Navy had at the time. Despite its serious limitations (short-range local monitoring, difficulty penetrating oceanic thermal levels, and various sailing limitations), it was seen by the Royal Navy before the war as Trump card.[31]

Only two years after the outbreak of the war the tactical use of location technology began in the form of "Huff-Duff" (HF/DF) direction finding devices on the decks of ships. After a number of attempts the FH4 direction finding system was developed which allowed the operator, through a visual indicator based on an electronic receiver, to point to the precise direction to a range of 20 miles of a submarine that emitted a brief radio transmission.

A Huff-Duff set fitted to HMS Belfast. These sets were common pieces of equipment by the spring of 1943. (Rémi Kaupp, Creative Commons CC-BY-SA)

The wolfpack tactic needed U-boats to communicate with each other. This created numerous opportunities to locate them, and the convoy commander needed only to send an escort ships a few miles outside the convoy in the direction of the detection in order to the locate the sub. At the very least this action would be enough of a threat to force the U-boat to dive. At the beginning of 1942, in most convoys there was a ship equipped with the Huff-Duff system, and at the end of 1943 every convoy had at least one such ship. [32] What made it so effective was the fact that the Germans continued to see their radio transmissions as immune from tactical location until the end of the war. According to the Germans, this would need to be based on triangulation, meaning the locating ship would have to change location as it was receiving the transmission. The U-boat service developed a system in which the message was recorded before being broadcast in a short transmission lasting only several seconds. The Germans did not estimate that precise directional location of the transmission, at a limited range, would suffice. However, in contrast to the German expectations, when convoys had multiple location sensors the commander could triangulate on his own, and work out the precise position of the U-boats. [33]

Another innovation in the sensors was the implementation of radar, initially, long wave (L band) and later short wave (S/X band) radar. In ideal conditions ship-borne short wave radar could locate U-boats on the surface at a maximum range of 3.1 to 4.3 km, and less in choppy seas. [34]  

 As mentioned previously, the U-boat force reacted to these innovations.[35] One well-documented tactic for overcoming the escort force's surface and sub-surface sensing ability was penetrating the convoy at night. This denied the sonar a subsurface target and prevented the radar and lookouts from identifying the submarine in the darkness of ocean between the silhouettes of dozens of ships. This is comparable in some ways to the tactic of using the civilian population in urban warfare. However, after it was identified, this tactic gave the escort ships a relatively close search area and high kill rates.[36]

Air patrols proved themselves as scouts, in addition to suppressing U-boat ability to sail on the surface. At night and in inclement weather, of course, the effectiveness of these patrols was nonexistent. At the end of 1941 the British placed radars on planes to identify submarines on the surface. Still, these radars lost their effectiveness when they approached their targets. Only with the use of Leigh Lights, specially designed spotlights, did the air patrols become truly lethal. The spotlights were thrown on only when the planes approached the targets and were locked directly on the target. The surprised U-boat crew only had a few dozen seconds to dive from the moment they were caught in the spotlight before they came under fire. The darkness suddenly turned from cover into a threat, and slowly the subs stopped sailing on the surface at night to charge their batteries. [37]

Underwater sensing was also used by planes further away from the convoys themselves, mostly on the basis of general intelligence on the location of wolfpacks. The planes dropped scattered hydrophones and miniature sonar systems on pontoons, which broadcast their location back to the plane in order to pinpoint the location of the submerged enemy sub. [38]

The complex of diverse sensors and its broad deployment around the convoy made every U-boat operation more dangerous for the submariners. Approaching a convoy could mean the exposure of a submerged sub by sonar, while doing so on the surface or at periscope depth could mean being revealed by an alert lookout or by the systematic sweep of the radar. Coordination between U-boats, which was vital for creating a coordinated attack, depended on radio transmissions. It was possible to pinpoint the transmissions, which brought about more sweeps by sonar and radar. In spring 1943, the scales were tipped against the submarines because of this complex of sensors. Submarine operations became too dangerous not only because of the escort force itself, but also further from the convoy sailing in the sea itself became dangerous. Sailing at night did not allow the submarine lookout on the bridge to spot incoming aircraft. Sailing during the day was interrupted repeatedly by VLR long-range air patrols, and aerial screens became more common both near the convoy and in the heart of the ocean. Escort carriers deployed tactical aircraft, initially 6 planes and later 24, which created a patrol screen on the basis of the situational picture that was continuously created.

The complex of multi-domain sensors (underwater, surface, and air), multi-spectrum (acoustic, radar, lookout) and at diverse ranges (LOS and NLOS)  finally pushed the U-boats from the heart of the sailing lanes to the margins of the naval campaign – to the South Atlantic and the Indian Ocean.

Reports from the escort ships, patrol planes, reports from decoding Enigma broadcasts, general intelligence on the U-boat force and radio direction finding were all concentrated in Western Approaches Command in Liverpool.[39] From there the convoys navigated into bypass lanes, and escort forces were concentrated as a reserve force ahead of an anticipated encounter with a submarine force. This was the operational-level control mechanism in the battle – a traditional mechanism that successfully concentrated information by new means.

But the most dramatic change occurred at the tactical level.  Until the war tactical communication between ships was done by signaling using spotlights and flags, with minimal radio transmissions. As long as naval warfare was waged between massive gunships this form of communication sufficed. But when they faced a concealed adversary the missions of forming a situational picture from shards of information spread between ships in the convoy, coordinating the tactics of U-boat hunting, protecting the rest of the ships, and saving crew members of damaged ships became too complicated for this form of communication.

A need emerged for better coordination on the tactical level among the escort force in order to create an organic force and communication that enabled piecing together an actionable situational picture. High-frequency radio-telephone communication, trained personnel, equipped escort forces, along with a clear command structure enabled this new way of operating.

WATU (Western Approaches Tactical Unit)[40] represents an example of an operational learning mechanism that concentrated information from battle, identified operational anomalies, and enabled the immediate enhancement of operational tactics. This was data-processing in its early analog form. The fact that a convoy vs. wolfpack battle sometimes lasted for days allowed WATU to seek and find possible explanations for operational phenomena and to offer tactical solutions during the battle through radio communication with the convoy. WATU wasn't only an information processing system during battle. It became the school for training naval commanders and for training the escort chain of command. More than 5,000 officers from all the Allies received their main tactical training there.

The emergence of the convoy against the wolfpack also rendered the central concept of naval firepower - big guns -  irrelevant. The only targets these guns had were a few German surface ships, which quickly disappeared from the fight. In 1939, depth charges were in effect the only weapon ships had against submarines. It turned out to be a weapon that indeed frightened submariners, but not one that was especially effective. Anti-submarine munitions launched from airplanes weren't any better. Though the planes' guns could penetrate the body of the sub, they rarely succeeded in surprising the U-boat in daytime in order to get in range. Depth charges dropped from planes didn't achieve impressive results either. Based on British analysis from August 1940, depth charges were only effective when they were dropped in the first 15 seconds after a U-boat dived beneath the surface. According to this study, 50% of the aerial attacks on subs were ineffective in terms of lethality. [41] At night it was even more difficult.

 It was only once their weapons were connected to the sensors that the submarine hunters achieved consistent success. There were two important developments that enabled this, underwater sonar-coordinated munitions and aerial radar coordinated munitions.

Underwater sonar-coordinated munitions

Depth charges were large mines wrapped in steel barrels, dropped into the sea from a special apparatus on the ship's stern. Numerous depth charges were launched in an attack and were set to detonate at different depths, with the damage being done by the blast wave of water striking the body of the sub. The catch was that such a blast could damage the ship itself and the equipment installed on its hull. The charges had to be dropped from the sides of the ship or its stern. Sonar, on the other hand, which worked on acoustics, could only operate a short, narrow beam in front of the ship, due to the noise of the propeller in the stern. This meant that using the ship's main anti-sub weapon involved maneuvering over the U-boat and losing sonar contact with it. U-boats captains quickly grasped this and took advantage of the time between the sounds of the sonar moving away and the stern of the ship moving over them in order to skip away.

The clumsy nature of depth charge handling on board meant that their number was limited, and loading between sets could take the better part of an hour, increasing the U-boats' chances of survival. The solution was to use a series of not-especially-impressive-looking weapons launched from the bow of the ship at a target. "Hedgehogs"[42], "Cuttlefish"[43], and "Mousetraps"[44]  were versions of multi-barreled mortars or a bunch of rockets with much smaller warheads, launched away from the bow. This category of weapons was based on creating a precise explosion of cluster munitions in the water, and achieved high rates of success, up to 62% in a single volley, far better than the 7% rate of depth charges. [45]

Aerial munitions

 The lack of relevant weapons greatly limited the effectiveness of air power in the battle at a critical stage in the war. Despite their limitations, depth charges were left as virtually the only option. Accompanied by radar, Leigh Lights made long-range bombers far more effective in dropping depth charges, and firing rockets or its cannons at submarines. [46] In November 1941, a plane equipped with the ASV-2 aerial radar succeeded in sinking a U-boat for the first time. By the end of that year, more than 300 Coastal Command planes were outfitted with this system. The ASV Mark III surface search radar sparked another revolution in finding and attacking subs from the air. In May 1943 planes sank 22 U-boats, while in July of that year the number rose to 31.[47] The main change was the ability of pilots to find targets before they could be seen, to close on them using radar and to attack them with precision using the Leigh Lights in conjunction with radar. During the war many other types of sensors were developed, as were weapons that operated with them, like the Magnetic Anomaly Detection attached to the nose of planes. This sensor could identify a metal body just below the surface, and could fire specially designed munitions. [48]

As effective as Coastal Command's VLR aircraft were with their new technology and concepts, they remained a small percentage of its air power. The command was the RAF's stepchild, seen as competition for precious resources with "Bomber" Arthur Harris's Bomber Command. The vital VLR bombers were allocated in this mindset, with perpetual foot-dragging in providing planes to Coastal Command.[49] Even when the air patrols, outfitted with radar and coordinated weapons systems, reached peak effectiveness protecting the convoys and were clearly crucial to their survival, the long-range bombers were still a rare commodity. The solution came in the form of escort carriers which could carry up to 24 planes. Carriers designed to escort convoys were initially improvised by outfitting a flight deck on merchant ships, before giving way to purpose-built carriers. These were far less impressive than the massive carriers at the start of war, or the famous carriers from the war in the Pacific. They mainly carried patrol planes armed with torpedoes and a few bombers. In time, larger escort carriers were developed. The carrier-launched planes enabled the locating and attacking of subs, and proved effective in protecting convoys from subs and from German planes.

U-848 under attack by a US Navy Consolidated PB4Y-1 Liberator in November 1943. (Crew of PB4Y-1 107-B-12 of VB-107, public domain)

By 1943 the Allies had put together a critical mass of escort carriers. Around 100 escort carriers were built and fought in the war in all the Allied fleets, and in 1943 alone 25 carriers entered the ranks of the Royal Navy. [50] The same year, the US Tenth Fleet, created to consolidate the anti-submarine warfare efforts, began putting together "hunter-killer" teams from escort ships and escort carriers. These teams were able to hunt subs, surprise wolfpacks, and allow the convoy escorts to maintain their defensive positions. They even began going out on offensive operations to break up ambushes based on SIGINT. The Tenth Fleet, under Rear Admiral Francis Low, reflected the American understanding about the need for organic multi-domain forces to defeat the underwater adversary. [51]  Attacks by the hunter-killer teams, at the heart of which were escort carrier-launched naval aircraft, sank 24 U-boats from April 1943 until the end of the year.

When British carriers escorted 14 convoys to Russia, for example, their planes achieved 66 identifications, carried out 73 attacks, and sank 13 U-boats. U-boats and German attack planes were driven off by the force. Another contribution, perhaps even more important, came from the coordination between air patrols and the anti-sub destroyers and frigates that were directed by the force to successful attacks. [52]

4.Contemporary Lessons from the Battle of the Atlantic

This study rests on the argument that the Battle of the Atlantic is extremely relevant for the IDF and Western militaries today. It relies on a core similarity between the disappearing or stealth enemy in the Atlantic Ocean during WWII, and the nature of enemies that Western militaries such as the IDF now face. The central claim here is that the area-denial tactics of a stealthy adversary was best countered by a multi-domain wide-spectrum complex of sensors, communications, data-processing and close air-support.

Since the 1990s, the IDF finds itself fighting on an "empty" battlefield, at least to the naked eye. IDF's precision fire caused the Syrian Army of the 1990s to undergo a process of replacing armored formations with infantry, and pushed enemies like Hezbollah and Hamas to develop operational concepts centered around avoiding exposure to Israeli firepower. The IDF's effort to adapt to this trend in recent decades has meant massive investment in improving its intelligence and targeting cycles, primarily from the air. The IDF increasingly understands that its operational intelligence-strike complexes are insufficient.[53] It recognizes the need to acquire the ability to locate the enemy during the land battle, where he is forced to operate and reveal himself. 

The IDF is also deeply involved today in developing a complex of sensors and information processing for the tactical ground forces. This idea undergirds the Precision Artillery Project (Chupat-Atar) in the ground forces concept "Land Ahead" (Yabasha-Ba'Ofek).[54] The US military's Multi-Domain Operations also points in the same direction.[55] Both militaries are concerned by "near-peer competitors" able to utilize technologies like precision missiles and electromagnetic spectrum warfare in order to disrupt maneuver, while reducing their own tactical exposure. [56]

So what are the relevant lessons for us from the Battle of the Atlantic?

A. Organizational Repression – In the interwar period, the Royal Navy simply refused to recognize the U-boat threat as a major challenge that demanded a new response. There were a variety of reasons for this. The British ASDIC sonar was a top-secret technological accomplishment, and was seen by the Admiralty as a decisive response to the challenge, despite its well-known limitations.[57] The interwar years saw a deep economic crisis, and the Royal Navy had to fight for its resources. The Admiralty, run by capital ship commanders, preferred to build battleships and cruisers. The European arms control agreements are evidence of this – they included limitations focused mainly on the German navy's capital ships. The Royal Navy wanted to refight World War I's Battle of In its determination, it treated the U-boat challenge as peripheral. It raised the classification level of anti-submarine research from WWI, thus preventing access to it. Later it even destroyed these lessons, which were called "irrelevant."[58] The literature also points at a rigid and hierarchical navy culture. This restricted the development of new conceptual approaches and a trial-and-error system.

There were also structural reasons for the British delay in reorganizing for modern naval warfare. [59] The establishment of the RAF greatly weakened the navy's ability to maintain effective pioneer naval aviation teams. The big carriers were expensive to build, and were seen as mere supporting forces for the surface gunboat formations. Challenges in its development made naval aviation, in a difficult resource environment, relatively easy to ignore.[60] As it turned out, naval aviation was the single most critical factor for the defeat of the U-boats in the Atlantic.  

A conservative organizational dynamic is not an invention of the Royal Navy. It is also applicable to the IDF today. How do we free ourselves from its grasp?

B. Focusing on the right threat - The U-boats posed a mortal threat to British shipping, so the British understood that the German submarines had to be defeated. But before the war, and for a significant portion of it, the Royal Navy focused on the problem it had prepared for – defeating the German surface fleet. The RAF, meanwhile, preferred to assume that strategic bombing of German cities would also solve the U-boat challenge without straying from the strategy it had already mapped out. It was only when the Allies organized convoys, built the Western Approaches Command as a fighting force with well-trained escort forces, and developed sensing technology and tactics for defeating submarines in the open seas, that they were able to make real progress against the U-boat threat.

Can the IDF adapt to the threat of fires-based warfare?  Can its operational-level attack complex orient itself toward defeating the rocket and missile threat on Israel? Does the IDF have the potential to be more effective than it is today? Has the IDF adapted adequately to the rocket and missile threat against Israel's military force themselves? Is the homefront air defense array – the only, entirely new realm the IDF developed against the rocket and missile threat – sufficient to defeat this new type of enemy attack?         

C. It's the sensors, stupid! (not size and firepower) – Even though everyone in the Israeli defense community talks about the stealth enemy, our investment continues to go into advanced combat platforms and weapons that are not part of an integrated sensors system. The British had to learn this lesson the hard way. In September 1939 the Royal Navy had 15 capital ships and another five under construction, seven fleet carriers (designed to aid the surface gunship fleet), 66 cruisers, and another 23 on the way. One hundred eighty four destroyers were operational, with around 50 ordered or under construction. Only 15 of them were fit for anti-submarine duties, with sonar and depth charges. Of the 50 destroyers under construction during that period, only around 20 were designed to protect convoys. Around 50 corvettes were under last-minute urgent order for anti-submarine escort missions.[61]

What types of ship did the Royal Navy add to its fleet during the war? Fifty eight escort carriers (which didn’t exist at all in the fleet in 1939), only 12 cruisers, 120 destroyers – almost all for escort duties, [62] around 240 frigates (designed for anti-submarine warfare), and 270 corvettes (also designed for anti-submarine warfare). [63] The list of anti-submarine ships speaks for itself – relatively cheap, easy to build ships designed for one mission were clearly prioritized over large surface warships from the moment the situation became clear. In the British navy itself (including the dominions) more than 1,000 such ships entered service in the war, while not one capital ship did. All that these ships – less armored, slower, and more lightly armed - were asked to do was to carry more electronic sensors and relatively simple anti-sub ammunition. In addition, the ability of carriers to provide air patrol cover relied on sensors.

In the IDF, despite new multi-domain concepts, new tanks, heavy and light APCs, and self-propelled howitzers dominate the IDF's land force design plan. These heavy platforms haven’t lost their importance, but at least some of them must change their purpose and form. More patrol and sensor platforms are needed, including those that carry sensor-equipped drones and missiles that are integrated with the area sensor network.

D. The tactical realm is the center of gravity - The Western Approaches Command managed the anti-submarine campaign during the entire war. From the beginning of the war the locating system developed initially from the coastal stations, and in 1941 the German Enigma code was also cracked. The centralized management of the broader campaign, rerouting convoys to less-threatened lanes, and initial air patrols from Coastal Command all contributed greatly to the campaign. Still, the unambiguous reason for the decisive turn in the campaign in May 1943 was the development of a significant escort-carrier force, which included air cover. At this stage, it wasn’t only that the escorts could accompany every convoy, but that they could also do so by a broad deployment of the force and a range of submarine sensors. The multiple means of sensing on the battlefield itself, the expertise of the escort formations in the new sensor warfare and the adjacent sensor and aerial attack dimension are the reasons for turning Doenitz's U-boats in May 1943 from the hunters into the hunted.

And where is the center of gravity in terms of sensing and information processing in the IDF? We still see sensing as a function for centralized intelligence gathering bodies, and information processing as a concentrated research process.[64] The function of tactical reconnaissance is still waiting for an update.

E. Organic tactical airpower – One of the most effective tools in the campaign against the U-boats was airpower. Some studies directly attribute the turning point in the campaign in April-May 1943 to the hunter-killer teams, which were centered around escort carriers. [65] The operational subordination of Coastal Command to the navy indeed improved the tactical coordination between air and sea. Still, an obvious barrier to the integration of the air force was the fact that in the UK, planes belonged to the RAF. Even with Prime Minister Winston Churchill emphasizing the gravity of the naval threat, the RAF continued to see the Atlantic campaign as secondary. The main effort of the air force was the strategic bombing campaign against German cities, which demanded long-range bombers in great numbers. Until December 1942 the number of Coastal Command VLR planes was never more than six, and in February 1943 it rose to 17. [66]  Strategic bombings, in the other-hand, used long-range bombers by their hundreds and thousands.[67] Statistics show that one long-range Liberator bomber, over an average service of 30 missions from its base in Iceland, could save more than six ships from submarine attacks. The alternative benefit of the same plane bombing Berlin was dropping 100 tons of bombs which would kill 24 people and destroy several homes. [68] Coastal Command itself sought offensive missions against submarines at the expense of escorting convoys.[69]  According to German statistics, despite a significant  British effort in the Bay of Biscay campaign, in the first five months of 1942 not a single U-boat was hit in French coastal waters.[70] This fact didn’t prevent the RAF from continuing to invest in similar patrols in 1943.[71] A comparison between the figures from February and November 1943 reveals that the escort planes were almost five times as effective in terms of U-boats destroyed than planes on independent submarine hunting missions. [72] The only advantage of the aggressive approach that the Coastal Command adopted was that it was economical in terms of long-range bombers, needed in Bomber Command.

A less economical approach in terms of bombers was used by the US Eighth Air Force in its bombing of submarine bases in France. In the course of a year, from October 1942 until October 1943, it carried out more than 2,000 bombing runs. The operation cost the US more than 1,000 airmen and 135 bombers. Despite the high price, the operation was a complete failure in meaningfully weakening the U-boat force or disrupting its operations, because of the bases' heavy protection. [73]

A glaring contrast to the lone aerial attacks approach was the establishment of the US Tenth Fleet. It contained the coastal air force, the escort ships, and escort carriers with their planes all under one command. The tactical effectiveness proved itself quickly. In the Royal Navy too, airpower only became meaningful on the battlefield with the arrival of the escort-carriers under direct command of the escort force captains or the commanders of the hunter-killer groups.

In the IDF, the vision of an Army "air force" consisting of drones was put forth by the IDF Ground Forces commander, Gen. Kobi Barak, in volume 11-12 of The Dado Center Journal. [74] Still, despite the entrance of these unmanned aerial vehicles (UAVs) into the IDF ground forces, the traditional balance between air and land forces in IDF has been preserved. The IAF continues to control the vast majority of air assets, including those designed for tactical use in land battle. "Escort carriers on trucks" – ground combat platforms whose main purpose is carrying a diverse and meaningful air element to the battlefield in support of the ground forces – still do not exist, and by all indications are not even on the drawing board.

F. Lethality – The enemy refuses to simply enter our sights. Locating the enemy in battle through contemporary intelligence means is generally insufficient to close the targeting cycle. The maneuvering force's firepower, generally not connected to sensors, is not fully utilized. Attack vessels that operate in coordination with sensors are needed. Their main virtue is not the size of the warhead but instead its speed and precision. We need a diverse armed sensor complex. In 1939, the RAF was the most deadly naval force in history. But its massive gunships quickly became easy prey for stealthy U-boats and raids by small planes. Depth charges, a technique used in WWI, proved ineffective, as did bombs dropped by planes. The change in terms of lethality came when escort ships were equipped with attack systems like "Hedgehogs" and "Cuttlefish" which could be used in concert with sonar. Attacks from planes became effective only with Leigh Lights and Angular Velocity Sights.[75]  

G. The tactical information revolution trends in our favor – The campaign in the Atlantic is described by some as a technological competition between two evenly matched sides that implement measures and counter-measures.[76] But a more critical look at this argument reveals that the competition trended toward the allies. The U-boats started the battle with most of their tactical potential already realized. The tactical advantage of diving and sniping from a distance with torpedoes was the manifestation of the engine, electric propulsion, and compressed air. None of these mechanical technologies went through a meaningful breakthrough during the war. The ability of submarines to improve their stealth tactics through a rigid signature regime (radio silence, underwater sailing) was rather limited, and imposed a significant cost in terms of effectiveness. The snorkel, a technical solution which entered service toward the end of the war in the form of a breathing tube that allowed continuous underwater sailing, was also incapable of restoring concealment. [77] Air patrols equipped with short-wave radar and lookouts could find surface maneuvers at night and the mast's wake during the day, while the snorkel itself significantly limited the submarine's maneuverability.

Electronics, on the other hand, was a revolutionary development. The ability to turn the potential of electronics into an entire world of innovative engineering in terms of sensors and communications was virtually boundless. Electronics were less helpful to the U-boats than they were to their hunters. U-boats, for example, were never outfitted with radar,[78] since it radiates to great distances and gives away its location. Ships - U-boat prey - were visible from a distance anyway. It wasn’t only that new electronic sensors were easier to develop than stealthier subs, but they were also much cheaper. For the price of one U-boat, it was possible to build, equip with sensors, train, and fly dozens of patrol planes. The U-boat force was forced to develop bigger, longer-range, and more expensive models during the war. The Type XXI U-boat was designed for much longer and faster underwater sailing thanks to its large body and impressive number of electric batteries it carried.[79] But even an expensive (and late) solution such as this didn’t contain sufficiently significant stealth potential in relation to the short-wave radar (against periscopes) and magnetic sensors.[80]

However, the Allies only needed to develop simple escort ships, which were cheap and fast to produce. Ships were still bigger and more expensive than U-boats, but in relation to each side's production capacity, within a few short years Britain and the US were able to build a sophisticated, widespread multi-domain anti-submarine network, which more than made up for the growth in the U-boat force they were facing. The Germans took advantage of the electronic competition and developed many radar detection technologies, but these made the submarine dive more often, reducing its effectiveness. The asymmetric "disappearing" side is far more sensitive to sensor and communication technological developments, and the age of electronics offered just that.

The IDF enjoys not only a clear material advantage over its enemies, but it also has far more technological potential. These sensor and information processing technologies are available to both sides (though Israel also enjoys an obvious advantage in its access to technology and its ability to develop weapons systems), but the potential in an operational context is different. IDF warfare is mainly out in the open, based on platforms on land, air, and sea. Israel's adversaries can improve their ability to gather intelligence and create a situational picture, and to more accurately aim their fire at IDF forces, but this is only an incremental improvement. Exposing our stealth enemy by an advanced sensor and information processing complex on the battlefield, on the other hand, means pulling the rug out from under his operational concept. Techniques like fighting in overgrown, urban, or underground areas using rockets, anti-tank and anti-aircraft missiles can still become more sophisticated, but it has largely exhausted itself. The adversary has fully utilized stealth and concealment techniques, while the IDF hasn’t even begun to scratch the surface of the tactical sensor/processing complex of the mobile-digital Age.

Conclusion

Today, Israel faces a strategic offensive from an enemy who aims its missiles at the Israeli homefront, while avoiding the IDF's full combat might. Stealth tactics on and beneath the battlefield on the one hand, and bursts of tactical area-denial fire against our forces on the other hand, describe the essence of the U-boats' advantage in WWI, and the IDF's challenge today. The Battle of the Atlantic represents therefore a valuable learning source for the IDF and Western militaries more broadly.

Electronics in WWII, and digitization today, contain potential rooted in sensors, communication, and information processing. In the technological realm, then, we have the opportunity to turn the tables on the side that seeks to hide.

Airpower played a critical role in cracking the U-boat challenge. The Battle of the Atlantic teaches us that the air dimension must be integrated with the tactical force itself, under one command. The RAF, even under great pressure, simply refused to divert significant efforts to the campaign at sea. Thirty-eight thousand bombers and almost seven thousand patrol planes were built during the war by Britain alone.[81] Still, at the height of the Atlantic campaign in spring 1943, there were only 49 VLR bombers in service in Coastal Command.[82]

Sensors can't replace platforms. The warships did not lose their place in the Atlantic battlefield, but unquestionably changed their role. More simple, cheap, and easy-to-produce  platforms entered the campaign, whose primary purpose was carrying sensor systems and weapons designed to operate with them. This meant less generic "lethality" of massive cannons and more precise, specially designed sensor-kill complexes. Our current force design vector is not moving in this direction.

Finally, the most important lesson. Britain paid a painful price in blood in order to learn. Considering that submarine warfare took place twenty years before, this was an entirely exorbitant learning cost. It was paid because of the consistent, determined, and well-documented refusal of the Royal Navy to deviate from its old customs and turn its attention from the massive warships to innovations like naval airpower, submarines, anti-sub ships and electronic sensors. 

Every historical parallel has its limitations. The world of big-data, in contrast to the world of electronic signatures in WWII, demands localized information processing. Another small difference in the IDF context is that we are not preparing for a war lasting five years. These conditions mean that we have to learn whatever we can from history. Our current enemies are similar enough, and the technological opportunity of the new digital age provides us an opportunity. Diverse, cheap, and small sensors, UAVs that can be integrated with the ground force in large numbers, wireless information networks and automatic information processing all provide us with the opportunity to create the relevant sensor-processing-attack complexes for our context. The disappearing enemy is extremely vulnerable to these innovations. Let us skip the bloody price of learning on our next field of battle. 

 

BG Eran Ortal is the commander of the IDF/J3 Dado Center for Interdisciplinary Military Studies.

[1] Holger H. Herwig, "The Submarine Problem - Germany, Britain and the United States 1919- 1939", in: Murray and Millet (eds.), Military Innovation in the Interwar Period, 243.

[2]Lazar Berman, "The Disruptors: How Conventional cosndierMilitaries are Challenged by Weaker Organizations – and How They Can Fight Back," The Dado Center Journal vol. 9, https://www.idf.il/media/26602/the-disruptors.pdf

[3] George Franklin, Britain's Anti-Submarine Capability 1919-1939 (Routledge, 2014), pp. 2-3, 186-188.

[4] John J. Abbatiello, Anti-Submarine Warfare in World War I: British Naval Aviation and the 6 Defeat of the U-boats (London: Routledge, 2011), 163.

[5] Karl Doenitz, The Submarine War )Hebrew translation( (Tel Aviv: Zmora-Bitan Modan, 1979), 32-33.

[6] Franklin, Britain's Anti-Submarine Capability 1919-1939, 108.

[7]  Winston Churchill, The Second World War, Volume 2: Their Finest Hour, (London: Cassell, 1949) 528-529.

[8] A. N. Other, "British and German Submarine Statistics of World War II", Naval Historical Review (Naval Historical Society of Australia, December 1972).

[9]John Terraine, Business in Great Waters (Barnsley: Pen & Sword Military, 2009), 768.

[10] A.N. Other and NHSA Webmaster, "British and German submarine statistics of World War II", Naval Historical Review, December 1972.

[11] G. Sheffield, "The Battle of the Atlantic: The U-boat Peril", BBC History, Updated 13 March 30, 2011, http://www.bbc.co.uk/history/worldwars/wwtwo/battle_atlantic _01.shtml.

[12] A. Roberts, The Storm of War: A New History of the Second World War (Penguin UK, 2009)

[13] H. R. Trevor-Roper, Hitler's War Instructions, Hebrew translation (Ministry of Defense-Publishing, 1992), 93-94.

[14] P. Edward Strong, Wargaming the Atlantic War: Captain Gilbert Roberts and the Wrens 18 of the Western Approaches Tactical Unit (MORS Wargaming, 2018), p. 4; Lindy Beige, The Wargamers who Won a Real War, Video, July 22, 2018, https://www.youtube.com/ watch?v=fVet82IUAqQ.

[15] Andrew Hendrie, Cinderella Service - RAF Coastal Command 1939-1945 (Pen & Sword 19 Aviation, 2006).

[16] R. F. Bennett, Behind the Battle: Intelligence in the War with Germany, 1939-45 (Sinclair- Stevenson, 1994).

[17] Martin T. Gilbert, Who Won the Battle of the Atlantic? (UK: Athena Press, 2007), 16.

[18] John R. Benedict, "The Unraveling and Revitalization of U.S. Navy Anti-Submarine Warfare", Naval War College Review 58, No. 2 (Naval War College Press, 2005), 96, https://digitalcommons.usnwc.edu/cgi/viewcontent.cgi?article=2206&context=nwc-review.

[19] Doenitz, The Submarine War Hebrew translation, 18-23.

[20] Terraine, Business in Great Waters,  265-268.

[21] Clark and Stillion, What it Takes to Win,  13.

[22] Charles M. Sternhell and Alan M. Thorndike, "Antisubmarine Warfare in World War II", OEG Report 51 (Washington D.C.: Navy Department, 1946), 83.

[23] Terraine, Business in Great Waters, 768.

[24] Norman Krahe, "Type VII U-Boat", WW2 Weapons, February 6, 2018, https://ww2-weapons. com/u-boat-type-7/.

[25] Doenitz, The Submarine War Hebrew translation, 51.

[26] Naval Staff History, The Defeat of the Enemy Attack upon Shipping 1939-1945, A Study in Policy and Operations, Vol. IA, (London UK: Admiralty Historical Section, 1957), 22.

[27] R. W. Burns, "Impact of Technology on the Defeat of the U-boat, September 1939 - May 1943", IEE Proceedings - Science, Measurement and Technology 141, Vol. 5 (IEE Press, 1994), 347.

[28] D. Syrett, The Defeat of the German U-boats: The Battle of the Atlantic (Columbia, S.C.: University of South Carolina Press, 1994), 11-12.

[29] Ronald Seth, The Fiercest Battle - The Story of North-Atlantic Convoy ONS-5 (London: Norton, 1962)

[30] Tom Linclau, "ONS-5", uboat.net, September 5, 2017, https://uboat.net/ops/convoys/ 38 convoys.php?convoy=ONS-5.

[31] Terraine, Business in Great Waters, 245, 264.

[32] Burns, "Impact of Technology on the Defeat of the U-boat, September 1939 - May 1943", 347.

[33] Syrett, The Defeat of the German U-boats, 11-12.

[34] Burns, "Impact of Technology on the Defeat of the U-boat, September 1939 - May 1943", 346.

[35] Doenitz, The Submarine War Hebrew translation, 166

[36] Strong, Wargaming the Atlantic War: Captain Gilbert Roberts and the Wrens of the Western Approaches Tactical Unit, 8-10.

[37] Burns, "Impact of Technology on the Defeat of the U-boat, September 1939 - May 1943", 349.

[38] A. Lambert, "Britain, Germany and the Battle of the Atlantic: A Comparative Study, by Dennis Haslop", Book Review, The Historian 78, Vol. 2. (New York, NY: Bloomsbury Press, 2016), 238.

[39] G. Mackenzie, "The Battle of the Atlantic - Western Approaches Command", Naval Historical Review (Naval Historical Society of Australia, 2001), https://www.navyhistory.org.au/thebattle-of-the-atlantic-western-approaches-command/.

[40] Strong, Wargaming the Atlantic War. The WATU was established as a wargames unit in 1942, headed by Gilbert Roberts, an experienced naval officer. Through primitive methods – chalk sketches on hardwood floors- Gilbert and his team of high school grads who excelled in math played out various scenarios involving the convoys. The main effort was "cracking the riddles"; for example, a report from an escort commander busy pulling survivors out of the water about a U-boat that is refraining from firing its torpedoes at the stationary target, or escort ships that are unable to find the attacking sub where it is expected to be – only a few thousand meters outside the convoy. Without concrete intelligence, the team created possible hypotheses about these anomalies. Acoustic torpedoes, which home in on the noise of the propeller, was the explanation given for the incident of the U-boat not firing on the stationary destroyer. The tactic of hiding within the convoy was also understood by the British through such a wargame. This was the logical explanation for the inability to find a target through sonar.

[41] Terraine, Business in Great Waters, 370-371.

[42] John Keegan, The Price of Admiralty: The Evolution of Naval Warfare (New York: Penguin .Books, 1990), 278.

[43] Geoffrey B. Mason, "World War II at Sea: Notes on Anti-submarine Weapons Used by Allied Ships", Naval History, 1992, http://www.naval-history.net/xGM-Tech-Anti-submarine%20Weapons.htm

[44] Sandy McClearn, "Canadian Navy Anti-Submarine Weapons and Torpedoes", Hazegray.org, updated August 4, 2017, https://www.hazegray.org/ ./navhist/canada/systems/asw

[45] Clark and Stillion, What It Takes to Win, 30.

[46] Burns, "Impact of Technology on the Defeat of the U-boat, September 1939 - May 1943", 349.

[47] Ibid, 346, 353.

[48] Winfield E. Fromm, "The Magnetic Airborne Detector", Advances in Electronics and Electron Physics, Vol. 4 (Academic Press, 1952), 258.

[49] Christina Goulter, A Forgotten Offensive: Royal Air Force Coastal Command's Anti-Shipping 66 Campaign, 1940-1945 (London: Frank Cass & co., 2005), 137.

[50] List of Escort Carriers of the Royal Navy", Wikipedia, The Free Encyclopedia, updated July 15, 2018, https://en.wikipedia.org/wiki/ List_of_escort_carriers_of_the_Royal_Navy.

[51] J. Barlow, "The Navy's Escort Carrier Offensive", Naval History Magazine, Vol. 27, No. 6 (US Naval Institute, 2013.

[52] Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 1939-1945: A Study on Policy and Operations, 296.

[53] General Aharon Haliva, "More of the Same The Need for Conceptual Leap in Force Design", The Dado Center Journal- Force Design - Part C (Hebrew)  (IDF: Dado Center, December 2016).

[54] Ami Rojkes Dombe, " IDF 2030: Small, Efficient & Lethal", Defense Israel (Hebrew), 16 November 2017, https://www.israeldefense.co.il/en/node/31785.

[55] Shmuel Shmuel, Lazar Berman et al., "Defining Multi-Domain Battle", The Dado Center Journal- Seventy Years of IDF Land Warfare (IDF: Dado Center, June 2018).

[56] Richard Fontaine and Julianne Smith, "Anti-Access/Area Denial Isn't just for Asia anymore", Defense One, April 2, 2015, http://www.defenseone.com/ideas/2015/04/anti-accessareadenial-isnt-just-asia-anymore/109108/.

[57] Franklin, Britain's Anti-Submarine Capability, 186-188.

[58] Herwig, "The Submarine Problem", 249.

[59] Jan M. Van Tol, "Military Innovation and Carrier Aviation", JFQ (NDU Press, Autumn/ Winter 1997-8), 107.

[60] Ibid.

[61] Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 89 1939-1945: A Study on Policy and Operations; National Museum of the Royal Navy, "British and Commonwealth Navies at the Beginning and End of World War II", Naval History, updated July 8, 2011, http://www.naval-history.net/WW2CampaignRoyalNavy.htm.

[62] National Museum of the Royal Navy, "British and Commonwealth Navies at the Beginning and End of World War II".

[63] Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 1939-1945: A Study on Policy and Operations.

[64] Eran Ortal, " Beyond the Wire – A New Business Model for AMAN," The Dado Center Journal volume 18 (Hebrew), (IDF: Dado Center, December 2018).

[65] Syrett, The Defeat of the German U-boats, 14-17.

[66] Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 1939-1945: A Study on Policy and Operations, 21.

[67] In the three days of the Dresden bombing in February 1945, no less than 1,300 VLR bombers took part, 800 of them British. Between 300-580 VLR British bombers took part in the dozens of aerial attacks on Berlin during the bombing of the city in the winter of 1943-44.

[68] Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 1939-1945: A Study on Policy and Operations.

[69] Ibid, 48.

[70] Ibid, 104.

[71] Clark and Stillion, What It Takes to Win, 31-32.

[72] Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 107 1939-1945: A Study on Policy and Operations, 24.

[73] Barrett Tillman, "Hard Targets", Air Force Magazine (February 2015), 81.

[74] Kobi Barak, "The Sky is no Longer the Limit", Dado Center Journal- Airpower - 50 years since Operation Focus (IDF. Dado Center, June 2017).

[75] Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 1939-1945: A Study on Policy and Operations, 21.

[76]  Clark and Stillion, What It Takes to Win

[77] Doenitz, The Submarine War Hebrew translation, 298.

[78] Syrett, The Defeat of the German U-boats, 3-4.

[79] Doenitz, The Submarine War Hebrew translation pages, 246-247.

[80] Chris Ashworth, RAF Coastal Command 1936-1969 (Patrick Stephens Ltd., 1992), 147.

[81] "Military Production During World War II", Wikipedia, The Free Encyclopedia, updated December 14, 2018, https://en.wikipedia.org/wiki/Military_production_during_World_ War_II.

[82] Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 1939-1945, a Study on Policy and Operations, 22-25.