What Lurks Beneath
Defeating a stealth enemy - Lessons from the Battle of the Atlantic
Eran Ortal and Lazar Berman
For decades, Western militaries have confronted a stubborn operational challenge. Our enemies disappear on the battlefield, and we struggle to bring our material superiority to bear. Simultaneously, our own maneuver makes us vulnerable to attack. How can we beat an enemy we can't see?
This study examines Allied anti-submarine warfare in WWII's Battle of the Atlantic, to extract contemporary lessons against stealth enemies. During the campaign, Germany attempted to blockade the British Isles through submarine attacks on Atlantic supply routes, using attrition through stealth area-denial tactics with concealed low-signature platforms.
This study deals first with interwar British operational learning, then examines the Atlantic struggle, before presenting Allied innovations in anti-submarine warfare. Finally, it lays out implications for contemporary force design against low-signature adversaries.
Learning, forgetting, and starting over
WWII was not Britain's first encounter with German submarine warfare. Facing a disadvantage in surface ships, Germany employed this revolutionary form of warfare in WWI. The submarine campaign was extremely effective, even leading to food rationing in Britain and her forces.
By 1918, the convoy system had been established, and the first underwater sensors had been developed. Moreover, the British had already used SIGINT from German codes and ELINT from submarine transmissions to hunt submarines and avoid ambushes.
WWI provided a blueprint for WWII, yet during the interwar period the world's leading navies continued to focus on surface fleets, the traditional measure of naval power. While all leading navies developed submarines and aircraft carriers, the Royal Navy considered them secondary supporting platforms.
The Allies had to relearn the lessons of the previous war, at great cost. "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," lamented Royal Navy Lieutenant Commander D.W. Water.
The Atlantic Campaign
Though the German surface fleet could not compete with the British, its submarine fleet quickly proved itself. The diesel-electric U-boats were effectively small boats armed with tube-launched torpedoes and a small gun. They mostly cruised on the surface. Submarines' strength lay in initiative—the ability to initiate or avoid an encounter—provided by stealth, not overwhelming firepower. The Type VII U-boat carried only 22 torpedoes, a light deck gun, and an anti-aircraft gun.  Like a sniper, it could hide until taking its shot, then break contact.
The Allies initially relied on depth charges, large mines dropped from the ship's stern to keep the blast from damaging the ship. Sonar, on the other hand, could only operate a short, narrow beam in front of the ship, due to the noise of the propeller in the stern. Using the ship's main anti-sub weapon meant maneuvering over the U-boat and losing sonar contact. U-boats captains quickly grasped this and took advantage of this gap between sensing and shooting to escape. The eventual solution was a series of successful bow-launched weapons.
The U-boat campaign peaked twice, in the "First Happy Time" (June 1940-December 1941) and "Second Happy Time" (Operation Drumbeat in early 1942). The U-boats' success hinged on Allied unpreparedness; many losses came while sailing unescorted just off the illuminated shores of the United States.  In November 1942, the rate of ships sunk matched that of new ships being produced in America, Canada, and the UK combined.
The British navy, with significant contributions from the Canadians, was responsible for protecting British shipping – without which it could not survive - and did so through regional commands, including the Western Approaches Command, based in Liverpool. The Royal Air Force (RAF) Coastal Command, originally designed to confront a German amphibious invasion, also played an important role, yet as the RAF "Cinderella", it suffered from a lack of long-range aircraft. 
The British Admiralty initially focused on offense, but failure forced a return to convoys, which the Canadians had instituted from the start of the war. A major deficit in escort ships limited this approach, making their construction an urgent priority. The British bought outdated American destroyers and new corvettes, whose easy production made them especially desirable. Eighteen months after entering the war, the US Navy established the Tenth Fleet for convoy escort and anti-submarine warfare in the Atlantic. 
Armed convoys dramatically limited the effectiveness of lone submarines. Germany was ready with "wolfpacks",  a U-boat screen spread across the Atlantic to identify convoys, and then coordinating by radio to concentrate and attack.
Successful submarine hunting hinged on detection. Scout planes could fly at high altitudes, cover large areas, find the submarine's wake and approach it before detection by U-boat lookouts. Beyond the immediate attack opportunity, detection provided the Royal Navy with its location and forced it to submerge, limiting its mobility. Western Approaches Command compiled the intelligence into a complete situational assessment, allowing convoys to avoid the U-boats. Until carrier-based forces were introduced late in the war, air patrols relied on Coastal Command,  which lacked sufficient patrol planes. 
Besides patrol planes and ships, the British had two other major sources of intelligence: Electronic Intelligence (ELINT) and code-breaking. ELINT-based location capabilities, called HF/DF (High Frequency Direction Finding) capitalized on submarine warfare's dependence on centralized operational management by radio to pinpoint the broadcasts and locate the submarine through triangulation.  Though insufficiently precise for hunting submarines, it did enable rerouting convoys away from ambushes. More famously, the cracking of the German Enigma code allowed the Allies to decipher messages from U-boats to their central command, including their precise locations.
The intelligence campaign alone could not achieve operational success. For that, the British required sophisticated battlefield sensors linked by high frequency radio to effective information processing capabilities and rapid learning mechanisms.
Four types of sensors set the course of the information battle in the Atlantic: observation, acoustics, radio direction finding (radiogoniometry), and radar. This system monitored broad swaths of the sea, hampering U-boats' efforts to approach the convoys.
In 1939, the Royal Navy had only 180 ships, mostly destroyers, equipped with active acoustic sensors (ASDIC), the only submarine-locating sensor in their arsenal. Two years later, the tactical use of location technology began in the form of "Huff-Duff" (HF/DF) direction finding devices on the decks of ships, allowing the operator to precisely locate a brief radio transmission to a range of 20 miles. Radar also helped locate surfaced U-boats.
In late 1941, the British placed radars on planes to identify submarines on the surface, but they were ineffective at close range. The addition of Leigh Lights, specially designed spotlights, made the air patrols truly lethal. Once the Leigh Lights locked on, the surprised U-boat crew had only a few dozen seconds to dive before they came under fire. The darkness suddenly changed from cover to threat. 
Further from the convoys, working off general intelligence on wolfpack locations, airplanes dropped 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 submarine. 
At the operational level, Western Approaches Command in Liverpool processed reports from escort ships, patrol planes, decoded Enigma broadcasts, general intelligence on the U-boat force, and radio direction findings, and directed convoys to avoid or counter-concentrated escorts against U-boats.
More radically, at the tactical level ships shifted from traditional naval communication by flags and lights to radio. Facing a concealed adversary, forming a situational picture from shards of information spread between ships in the convoy required better communication and coordination on the tactical level. High-frequency radio-telephone communication, trained personnel, and equipped escort forces, along with a clear command structure enabled this new way of operating.
The submarine hunters only achieved consistent success by linking their weapons to sensors, in particular through underwater sonar-coordinated munitions and aerial radar coordinated munitions.
Lack of relevant weapons initially limited the effectiveness of air power. Despite their limitations, depth charges remained virtually the only option. Combined with radar, Leigh Lights made long-range bombers far more effective in dropping depth charges and firing at submarines.  In November 1941, a plane equipped with the ASV-2 radar sunk a U-boat for the first time, and soon more than 300 Coastal Command planes were outfitted with the system. The ASV Mark III surface radar was also extremely effective. In May 1943, planes sank 22 U-boats, and in July the number rose to 31. Now pilots could find targets before they could be seen, close and attack with precision in conjunction with radar. The Allies developed many other types of sensors and the weapons that operated with them, like the Magnetic Anomaly Detection which could identify a metal body just below the surface and fire specially designed munitions. 
As effective as Coastal Command's VLR (Very Long Range) aircraft were with their new technology and concepts, they remained a small portion of its air power. The command was seen as competition for precious resources with Bomber Command, leading to perpetual foot-dragging in providing VLR bombers to Coastal Command. Escort carriers provided the solution. They mainly carried patrol planes armed with torpedoes and a few bombers.
By 1943 the Allies had a critical mass of escort carriers.  The same year, the US Tenth Fleet, created to consolidate the anti-submarine efforts, began putting together "hunter-killer" teams of 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 based on SIGINT. Perhaps more importantly, air patrols coordinated with anti-sub destroyers and frigates, directing the force to successful attacks.  The Tenth Fleet reflected the American understanding about the need for organic multi-domain forces to defeat the underwater adversary. 
In spring 1943, the Allies' sensor array combined with air-patrols tipped the scales against the U-boats. The Germans lost almost half their operational force in less than a month, forcing Doenitz to temporarily withdraw his forces from the ocean.
The array of multi-domain (underwater, surface, and air) and multi-spectrum (acoustic, radar, optical) sensors at diverse ranges (LOS and NLOS) ultimately pushed the U-boats from the heart of the sea lanes to the naval margins, the South Atlantic and Indian Ocean.
What lessons can we learn from the Battle of the Atlantic?
- Organizational Repression: Between the wars, the Royal Navy refused to recognize the U-boat threat demanded a new response for a variety of reasons: The British Admiralty saw their top-secret ASDIC sonar as suitable; competition for resources; a rigid and hierarchical navy culture; a preference to build battleships to refight WWI's Battle of Jutland. It raised the classification level of anti-submarine research from WWI, reducing its accessibility, and later destroyed many of these lessons as "irrelevant."
Structural reasons also delayed British reorganization for modern naval warfare.  The establishment of the RAF greatly weakened naval aviation innovation. Big carriers were expensive and seen as mere support for surface gunboat formations. Furthermore, development challenges made naval aviation relatively easy to ignore.
Today, the IDF suffers similar conservative organizational dynamics. How do we escape their grasp?
- Focusing on the right threat: Before—and during much of—the war, 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 would win the war. The Allies only really progressed against the U-boat threat by organizing convoys, creating the Western Approaches Command as a force with well-trained escorts, and developing sensing technology and tactics.
Can the IDF adapt to the threat of fires-centric warfare and orient itself against the rocket and missile threat facing? Does it have the potential to increase its effectiveness? Is the air defense array—the only, entirely new realm the IDF developed against the threat—sufficient to defeat this new type of attack?
- It's the sensors, stupid!: Britain prioritized relatively cheap, easy to build ships designed for one mission over large surface warships once it understood the situation. These ships traded armor, speed, and armament for more electronic sensors and relatively simple anti-sub ammunition.
Despite talking about the stealth enemy, we invest in advanced combat platforms and weapons unconnected to integrated sensor systems. Despite new multi-domain concepts, tanks, APCs, and howitzers dominate the IDF's land force design plan. Though these heavy platforms remain important, at least some must become sensor platforms, including carrying sensor-equipped drones and missiles integrated with the area sensor network.
- Stand-in tactical capability: Ultimately it was the significant escort-carrier force that turned Doenitz's U-boats from hunters to hunted.
The IDF still regards sensing as a function for centralized intelligence gathering bodies, and information processing as a concentrated research process. Tactical reconnaissance—as a potential center of gravity— begs for an update.
- Organic tactical airpower: Airpower was among the most effective tools against U-boats. Organizing Coastal Command under the navy improved tactical coordination between air and sea, yet British planes' subordination to the RAF, who preferred to focus on strategic bombing, remained a barrier to integration. By contrast, until December 1942 the number of Coastal Command VLR planes never exceeded six, but in February 1943 rose to 17.  Statistics show one long-range Liberator bomber, over an average service of 30 missions, could save more than six ships from submarine attacks. Coastal Command too preferred ultimately ineffective offensive missions against submarines to escorting convoys. Comparing data from February and November 1943 reveals escort planes to be almost five times as effective as independent submarine hunting. 
By contrast, the US Tenth Fleet concentrated coastal air force, escort ships, and escort carriers under one command. The tactical effectiveness proved itself quickly. For the Royal Navy too, effective airpower required escort-carriers under direct command of escort force captains or hunter-killer group commanders.
In the IDF, Ground Forces commander Gen. Kobi Barak proposed a drone-based Army "air force."  Though ground forces have some UAVs, the IAF still controls most air assets, including those for tactical use in ground combat. Land "escort carriers"—ground combat platforms organically carrying aerial support—do not yet exist, even on the drawing board.
- Lethality: The Allies needed simple weapons systems in conjunction with sensors for effective lethality against submarines, in lieu of the "big guns" of old. Similarly, today our enemy hides, and our intelligence cannot target him, preventing full utilization of our firepower. The IDF needs sensors coordinating with fast, precise attack systems rather than traditional artillery and air-power lethality.
- The information revolution favors us: The technological competition trended toward the Allies. U-boats began with most of their potential already realized, with only limited room for tactical or technological improvement. By contrast, the electronics revolution facilitated significant improvements in sensors and communications, both easier to develop and cheaper than the submarines they combated. The asymmetric side is far more sensitive to sensor and communication technological developments, and the Allies capitalized on the age of electronics to build a sophisticated, widespread multi-domain anti-submarine network, which more than compensated for growth in the U-boat force.
The IDF enjoys not only a clear material advantage, but also far more technological potential and an operational context suited to exploiting it. While Israel's stealth adversaries can incrementally improve their intelligence gathering and precision fire capabilities, exposing them using advanced sensor and information processing arrays undercuts their entire operational concept. While the adversary has largely exhausted stealth and concealment techniques, the IDF has barely scratched the surface of the tactical sensor/processing potential of the mobile-digital Age.
The Battle of the Atlantic is deeply relevant for the IDF and Western militaries today. There is a fundamental similarity between the stealth WWII enemy in the Atlantic, and the nature of enemies that Western militaries such as the IDF now face. The area-denial tactics of a stealthy adversary is best countered by a multi-domain ISR array 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 replace 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 has meant massive investment in its intelligence and targeting cycles, primarily from the air. The IDF increasingly understands the inadequacy of its stand-off intelligence-strike systems, and recognizes the need to locate the enemy using stand-in assets during the land battle, where he is forced to reveal himself.
The IDF is also deeply involved in developing a system of sensors and information processing for the tactical ground forces. This idea undergirds the ISR organization (Chupat Atar) in the ground forces concept "Land Ahead" (Yabasha Ba'Ofek). The US military's Multi-Domain Operations also points in the same direction. Both militaries are concerned by near-peer competitors using technologies like precision missiles and electromagnetic spectrum warfare in order to disrupt maneuver, while reducing their own tactical exposure. 
Digitization today increases the potential of sensors, communication, and information processing, which leverage the vulnerabilities of our stealthy adversary, and integrating air capabilities into the tactical force provides the platforms to bring those sensors to bear. Sensors cannot replace platforms, but can change their role, replacing generic "lethality" of massive cannons in favor of more precise, specially designed sensor-killer systems. Unfortunately, our current force design vector is not moving in this direction.
Most importantly, Britain paid for its education in blood because of institutionalized conservatism and an unwillingness to embrace innovative technologies and tactics. We don't have to make the same mistakes. Let us skip the bloody price of learning on our next battlefield.
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 Ibid, 346, 353.
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 Naval Staff History Second World War, The Defeat of the Enemy Attack Upon Shipping 1939-1945: A Study on Policy and Operations, 21.
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 Ibid, 104; Barrett Tillman, "Hard Targets", Air Force Magazine (February 2015), 81.
 Ibid, 48.
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 Kobi Barak, "The Sky is no Longer the Limit", Dado Center Journal- Airpower - 50 years since Operation Focus (IDF. Dado Center, June 2017).
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