The Battle of the Atlantic was the longest single campaign of the Second World War. Lasting from the very first day of the war in Europe to the very last, the battle pit German U-boats against Allied merchant shipping in a struggle for control of the Atlantic sea lanes, essential to keeping the British Isles supplied with food, fuel, and other raw materials. So vital was this lifeline to Britain’s survival that Winston Churchill would later write:

“The only thing that ever 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.”

Throughout the conflict both sides suffered dramatic reversals of fortune, until late 1943 when the Allies finally wrested control of the Atlantic from the Germans. While this success is often attributed to the introduction of superior weaponry such as escort carriers, long-range patrol aircraft, and radar, the real key to victory was doctrinal, with the Allies learning through trial and error how best to use tactics and technology to counter and neutralize the U-boat menace. And pivotal to this learning process was a unique unit of young women who, for three years, spent nearly every day holed up in an attic in Liverpool playing out elaborate combat scenarios with model ships on the floor. They were the Western Approaches Tactical Unit, or WATU, the war gamers who helped win a real war.

Almost the moment war was declared on September 3, 1939, the German Navy or Kriegsmarine launched a campaign of unrestricted submarine warfare against Allied merchant shipping in the Atlantic. Its goal was to starve Britain into submission and bring its leaders to the negotiating table, and early on it seemed as though the Germans might just succeed. Between July and October 1940 U-boats sank nearly 1.5 million tons of Allied shipping, and by 1941 had reduced Britain’s yearly imports from a pre-war total of 68 million tons to a mere 26 million tons. In 1942, Admiral Karl Dönitz, head of the U-boat arm, calculated that if he could inflict sustained losses of 700,000 tons per month, Germany would win the war.

What makes these losses even more staggering is the fact that unrestricted submarine warfare was nothing new, the Imperial German Navy having employed the exact same strategy some 20 years before. However, a number of factors resulted in the lessons of the Great War falling by the wayside. Among these was the British Admiralty’s inherent disdain for submarines, which First Sea Lord Sir Arthur Wilson had infamously dismissed as “underhanded, unfair, and damned un-English.” Consequently, Royal Navy doctrine in the interwar years barely mentioned submarines at all, and the strategy of grouping merchant shipping into convoys – which had proven so effective against U-boats during the First World War – had largely been abandoned by the start of the Second. Adding to the Admiralty’s woes was the loss of their naval bases in Ireland in April 1938 and the German occupation of France in May 1940, which simultaneously limited British access and increased German access to Britain’s vital Western Approaches.  It was also hamstrung by its rigid command structure wherein warship commanders were given very little individual initiative, leading to convoy escorts being lead on frequent wild goose chases on orders from shore.

But even after the Royal Navy managed to reorganize itself into a more effective anti-submarine force, it still faced the problem that although British naval doctrine had not moved on since 1918, German doctrine had. During the First World War, German U-boats had operated alone, with each commander seeking out and sinking targets on his own initiative. This approach, however, had been rendered ineffective by the introduction of the convoy, so between the wars the German Navy developed the rotte, or “wolf pack” tactic. In this system, U-boats patrolled in extended lines across known convoy routes. When a U-boat located a convoy, it would radio in its position to headquarters, which would then order the whole pack to converge on the convoy and attack as a group, overwhelming the escorts. While the Allies were aware of this overall strategy, they did not know exactly how U-boat wolf packs approached and attacked convoys. And aside from a few enterprising individuals like Frederic “Johnny” Walker and Clarence Howard-Johnson, few escort commanders possessed effective tactics for protecting their convoys and sinking U-boats when attacked.

To help solve this problem, in January 1942 Admiral Cecil Usborne formed the Western Approaches Tactical Unit or WATU, a dedicated war gaming and analysis organization under the command of Commander Gilbert Roberts. A career officer who had joined the Navy as a cadet at the age of 13, from 1935 to 1937 Roberts studied at the Portsmouth Tactical School where he became an avid practitioner of war games, especially those developed by Frederick T. Jane, founding editor of the famous Jane’s military reference guides. In 1937 Roberts was given command of the destroyer HMS Fearless, which was sent to patrol the Iberian coast during the Spanish Civil War. In October 1938, however, he was diagnosed with tuberculosis, declared medically unfit to serve at sea, and forced to retire from the Navy.

Roberts’s posting to the WATU proved fortuitous. Not only was he an avid war gamer and a skilled communicator, but according to author Terence Robertson:

“It seemed that by design or accident all the misfits of the navy had congregated at Liverpool Among his brother officers were many of his own kind—“passed overs”— who at some stage or other had become red-tape rebels But the vast majority were officers of the Royal Naval Volunteer Reserve, week-end sailors churned out by the recruiting machine often with inadequate training The Royal Naval Reserve, those independent merchant men who would become sore boils in big ship wardrooms, somehow fitted in here by providing their expert seamanship to balance the ignorance of the willing, but the lamentably “green.”

However, Roberts’s colleagues and staffers described him as a difficult man to work with – stubborn, demanding, and argumentative. But whatever his faults, his work with the WATU would prove decisive in securing Allied victory in the Atlantic.

Housed on the top floor of the Western Approaches Command Headquarters in Derby House, Liverpool, the WATU was mainly staffed by members of the Women’s Royal Naval Service, or “Wrens,” many of whom were as young as 17 at the time of the unit’s founding. Some, Like Laura Howes and Janet Okell, were hired for their mathematical or tactical skills; others, like Nancy Wales, for their proficiency in team sports – in Wales’s case, hockey. 66 Wrens in total would serve in the unit between 1942 and 1945.

The WATU’s task was to play through both actual and hypothetical encounters between convoys and U-boat wolf packs in order to work out the tactics used by the Germans and develop potential countermeasures. This was done on a large playing surface laid out on the floor in the largest room in the building, which was divided into ten-inch squares each representing a nautical mile. Merchant ships, escorts, and U-boats were represented by small wooden models, each of which was given precise attributes based on their real-life counterparts, such as maximum speed, minimum turning radius, and sonar, radio, and weapons range. Wrens playing as escorts stood behind cloth screens and could only view the board through small peepholes, while those playing as U-boats were given an unrestricted view. To further complicate matters, lines representing the courses of U-boats were traced in green chalk, nearly invisible against the brown floor, while the courses of the merchantmen and escorts were traced in white. Each team was given two minutes to confer and issue their orders, which were conveyed using slips of paper to prevent the other team from overhearing. The Wrens quickly became ruthlessly efficient at their jobs, with 19-year-old Janet Okell defeating Western Approaches Commander and WWI submarine veteran Admiral Max Horton no less than five times in simulated combat.

One of the first problems solved by WATU was how U-boats were managing to sink merchantmen in the interior of convoys. At first, naval planners assumed that the U-boats were attacking from the outside of the convoy as they had during the First World War, but given that escorts operated up to five thousand yards out from the convoy and German torpedoes only had a range of 5,400 yards, this seemed unlikely. By replaying past convoy battles, WATU determined that the U-boats were actually attacking the convoy from within, approaching from behind while surfaced and using their superior speed and the cover of darkness to slip past the escorts unnoticed. In response, the WATU developed a counter-strategy known as Raspberry, whereby upon a ship being torpedoed, the escorts to the sides and rear of the convoy would fall astern into a line abreast and drive forward blasting their sonar, while the forward escorts would zig-zag ahead of the convoy. This would effectively trap the infiltrating U-boat, all but guaranteeing its destruction. The tactic’s name came from Wren Jean Laidlaw, who likened the maneuver to “blowing a raspberry at Hitler.”

Another tactic developed by WATU, code-named Pineapple, was intended for use against U-boats lying in wait ahead of the convoy. Upon detection of the U-boat, the escorts were to steam ahead at full speed for 15 minutes, blasting their sonar and firing star shells, before falling back into their regular positions. This would in theory scare off the U-boat and prevent it from observing and reporting other escort tactics like Raspberry. When this tactic was first demonstrated to a visiting Royal Canadian Navy officer, he pointed out that the diagram looked rather like a pineapple, and the name stuck.

Another tactic called Beta Search used the opposite approach. Once the U-boat was detected, one escort ship was to advance towards it without using its sonar, firing star shells, or dropping depth charges. If, as predicted, the U-boat submerged, the escort would sail over it, tricking the U-boat Captain into thinking he hadn’t been spotted. But a submerged U-boat was far slower than a surfaced one, making it vulnerable to the rest of the escorts, who, under the cover of the convoy, would advance and drop depth charges on the U-boat’s predicted position.

In late 1943, Roberts began receiving reports that U-boats had begun targeting the escorts themselves. These attacks, however, were highly unusual; though in every case the escort spotted the U-boat and turned towards it, they were somehow always torpedoed from behind. Roberts realized that the Germans had developed an acoustic torpedo, which homed in on the sound of a ship’s propellers. This torpedo, which the Germans called the T5 Zaunkönig the Allies the German Navy Acoustic Torpedo or GNAT, was first deployed in August 1943 and threatened to tip the balance of power in the Atlantic in favour of the U-boats. However, in an inspired bit of deduction Roberts predicted that the torpedo’s acoustic could only track targets inside a 60-degree cone directly ahead of it, and developed a tactic known as Step-Aside to exploit this weakness. Upon spotting a surfaced U-boat, an escort was to fire a star shell, announcing to the U-boat that it had been spotted and forcing it to submerge and fire its torpedo. The escort would then make a hard 150-degree turn and accelerate to full speed, placing it outside of the torpedo’s acoustic cone, before homing in on and attacking the submerged U-boat. Along with decoy noisemakers called Foxer and CAT which were towed behind escorts to deflect acoustic torpedoes, Step-Aside effectively negated any advantage granted by the new technology.

In addition to developing new antisubmarine tactics, the WATU also ran regular training courses to teach these tactics to naval officers. Starting in February 1942, these courses ran six days a week every week until July 1945. In total over 5000 personnel participated in these courses, including officers from RAF Coastal Command and allied nations such as the United States, Canada, New Zealand, South Africa, Australia, Poland, Norway, and Free France. WATU also compiled regular memos known as Atlantic Convoy Instructions which were distributed to every escort ship operating in the Atlantic. In this manner Western Approaches Command was able to keep pace with changes in German doctrine and stay one step ahead of the U-boats. The results were dramatic: from 120 ships sunk in October 1942, by December losses had fallen to only 76 and continued to decline steadily thereafter. The success of WACU inspired the creation of sister organizations in Londonderry and Belfast, Northern Ireland; Irwell and Osprey in Scotland; Halifax in Canada; Freetown in Sierra Leone; and Bombay in India. But perhaps the greatest testament to the unit’s effectiveness was the fact that in U-boat headquarters in Flensburg, Germany, Admiral Dönitz hung up a photograph of Commander Gilbert Roberts with the caption:

“This is your enemy, Captain Roberts, Director of Anti U-boat Tactics.”

By May 1943, a combination of new tactics, larger numbers of escort carriers and long-range patrol aircraft, radar and direction-finding technology, and the reading of German Naval Enigma traffic had made U-boat losses unsustainable, forcing Admiral Dönitz to largely withdraw his fleet from the North Atlantic. Though submarine operations would continue until the bitter end, the U-boat arm would never again be the formidable force it once was in the first three years of the war.

Following the end of major U-boat operations in the Atlantic, WATU switched to developing anti-submarine tactics in support of the D-day landings in June 1944. Once again they were highly successful, with relatively few Allied ships being sunk by U-boats in the English Channel before the end of the war in Europe in May 1945. The Western Approaches Tactical Unit officially ceased operations two months later, having played a pivotal role in keeping the Atlantic sea lanes open and the Allied war machine marching towards victory. In recognition of their efforts, in July 1945 Admiral Horton sent the following message:

“On the closing down of WATU I wish to express my gratitude and high appreciation of the magnificent work of Captain Roberts and his staff, which contributed in no small measure to the final defeat of Germany. You had a great deal to do in winning the war because if we hadn’t won the Battle of the Atlantic we should undoubtedly have lost the war!”

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