Western Approaches Tactical Unit

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The crest of WATU, affixed to the entrance door.

The Western Approaches Tactical Unit (WATU) was a unit of the British Royal Navy created in January 1942 to develop and disseminate new tactics to counter German submarine attacks on trans-Atlantic shipping convoys.[1] Led by Captain Gilbert Roberts, it was principally staffed by officers and ratings from the Women's Royal Naval Service (Wrens).[2] Their primary tool for studying U-boat attacks and developing countermeasures was wargames.


During World War 1, U-boats (German submarines) sank merchant ships in the Atlantic Ocean so as to deny supplies to its enemies in Europe. Britain reacted by organizing the merchant ships into convoys escorted by warships armed with depth charges. This defensive system proved effective at repelling U-boats. During the inter-war years, Germany secretly developed new submarine tactics to counter the convoy system. The products of this research were the "wolfpack" tactics, wherein submarines would attack convoys in groups. Britain, by contrast, had neglected to study submarine tactics during the inter-war years. They entered World War 2 assuming that the Germans would operate much as they had during the previous war, unaware that the Germans would come at them with new tricks.

As soon as Britain declared war on Germany (3 Sept 1939), Germany sent its U-boats to attack trans-Atlantic shipping. The U-boats had a devastating effect. In 1938, Britain had received 68 million tons of imports, but in 1941 the U-boats reduced this to 26 million.[3] Britain was not a self-sufficient nation, and eventually its reserves of food would run out and it would be forced to capitulate to prevent a famine.[4] In March 1941, Prime Minister Winston Churchill declared that Britain was fighting "the Battle of the Atlantic", and made anti-submarine warfare a top priority.

The Royal Navy understood, from intercepted radio transmissions, that the U-boats were operating in coordinated groups, but did not know the specifics of their tactics.[5] On 1 January 1942, Admiral Cecil Usborne assigned Commander Gilbert Roberts to establish a wargaming unit at the Western Approaches Command in Liverpool, to analyze the submarine attacks and develop defensive tactics.[6] Roberts had played naval wargames during a two-year stint at the Portsmouth Tactical School, using them to develop new strategies and tactics. Additionally, Roberts was a gifted communicator who would be able to train commanders in the tactics he was to develop.[7]

Roberts moved to Liverpool to set up his tactical unit on the top floor of the Western Approaches headquarters. Most of the staff at Western Approaches were women from the Women's Royal Naval Service (colloquially referred to as "Wrens"), and likewise Roberts recruited most of his staff from the Wrens. At total of sixty-six Wrens served at WATU from 1942 to 1945.[8]

Roberts and his team reviewed battle reports from convoy escort commanders, recreated the battles in wargames in order to deduce how the U-boats were operating, and then devised tactics by which the escorts could defeat the U-boats. Their first product was a tactic codenamed Raspberry, developed that January (see below). As well as devising tactics, WATU also trained naval officers in their use by having them participate in wargames. The first batch of trainees arrived on 2 February 1942. The training course lasted six days, from Monday to Saturday, and was held every week from February 1942 to the last week of July 1945. Up to fifty officers at once took the course.[9] WATU not only trained British officers, but also officers from other countries such as Canada, New Zealand, Norway, South Africa, Poland, and Free France. On Sundays, Roberts occasionally demonstrated his wargames to visiting Americans,[10] but no American officers actually took his course. The American admiral Ernest King did not permit any American officers to take the course as he disliked the British Royal Navy.[11]

In May 1943, Admiral Doentiz ordered the wolfpacks to withdraw from the Atlantic, effectively ending the Battle of the Atlantic. In 1944, food imports to Britain rose to 56.9 million tons.[12]


What makes WATU an extraordinary episode in the history of military wargaming is that it used wargames to investigate real scenarios that were occurring during an ongoing war and develop solutions that were immediately implemented in the field. By contrast, most wargames are played during peacetime to prepare officers for potential wars, and the scenarios they explore are either hypothetical or happened many years ago, and may not be relevant to the next conflict when it comes due to unforeseen factors such as new technology or rules of engagement. In the 19th century, the Prussian military had been playing wargames for over forty years before they finally got their chance to test their mettle against the Austrians in 1866 and the French in 1870. The Prussians won those wars, but historians doubt how far wargaming contributed to their victories, because it is impossible to isolate their wargames' effect from other developments such as new technology, economics, differences in command structure, socio-political reforms, infrastructure, etc.


Western Approaches Command was an operational command of Britain's Royal Navy, tasked with safeguarding British shipping in the Western Approaches (the seas to the west of Ireland and Britain). Initially headquartered in Plymouth, on the southern coast of Britain, it was moved north to Liverpool in February 1941. After France had fallen to the Germans, North Atlantic shipping convoys had been diverted around the north of Ireland to evade the German navy. Relocating Western Approaches Command to Liverpool sped up communications. Its headquarters was Derby House, a building located behind Liverpool's town hall; today it's a museum.[a] The top floor, comprising eight rooms, was allocated to WATU.[13] Most of the staff at Western Approaches HQ were women from the Women's Royal Naval Service. Colloquially, they were referred to as "Wrens". When Roberts arrived at Western Approaches in January 1942, its commander-in-chief was Admiral Percy Noble, who was replaced by Admiral Max Horton in November 1942.

Staff and students[edit]

Captain Gilbert Roberts, director of WATU.

A total of sixty-six women from the Women's Royal Naval Service (Wrens) served at WATU from 1942 to 1945.[8]


  • Gilbert Howland Roberts - Director of WATU. Once commanded the destroyer HMS Fearless, but contracted tuberculosis in late 1937 and was barred from serving at sea.[14] Initially a commander when taking charge of WATU, he was promoted to captain in January 1942 by Admiral Noble after the Raspberry tactic was developed (see below). Was made a CBE in recognition of his contribution to the war effort through WATU.
  • Laura Janet Howes - Wren officer. Born in Antigua. Mathematical prodigy.
  • Elizabeth Drake - Wren officer. When WATU was established, she was already working at Derby House as a plotter.
  • Nancy Wales - Wren officer. Born in Kingston upon Hull, joined the Wrens in 1941. She was a passionate hockey player, and was selected for her understanding of team tactics.
  • Jean Laidlaw - Wren officer. Former Sea Ranger and chartered accountant.
  • Janet Okell - Wren rating. She was only 19 years old when she joined WATU in January 1942. She served at WATU for the whole duration. Okell was initially trained as a plotter, but she was soon participating in wargames as a player, commanding U-boats and escort ships alike.


Overview of the wargames[edit]

Gilbert Roberts was first introduced to wargaming during a stint at the Portsmouth Tactical School from 1935 to 1937. Roberts took to wargaming with great enthusiasm, and developed his own rulesets. Roberts' wargames were based on the wargames developed by Fred T. Jane in 1898 (Jane Naval Wargame and Fighting Ships).[15] Despite the strong effect that U-boats had during World War 1, Roberts' wargames at Portsmouth did not simulate submarine warfare, nor attacks on merchant convoys. In fact, nobody in the Royal Navy studied submarine warfare through wargames until the establishment of WATU in 1942.[16]

At WATU, the wargames were conducted in the largest room of the top floor of Western Approaches HQ. The floor was covered with brown linoleum and in the center was a painted grid. This grid was the game board. The gridlines were spaced ten inches apart, representing one nautical mile. Around the grid were vertical screens of canvas that had peepholes cut into them. The players who controlled the escort ships had to stand behind the screens and could only view the game board through the peepholes. The players who controlled the U-boats did not stand behind the screens and had an unrestricted view of the game board. The ships and surfaced U-boats were represented on the game board by tiny wooden models.[17] The U-boats' movement lines were drawn in green chalk, a color which contrasted poorly with the brown tint of the floor; and when viewed from an angle, these lines were practically invisible, so the players behind the screens couldn't make them out. The escort ships' movement lines were drawn with white chalk, which could be clearly perceived by the players behind the screens.[18] Players were given two minutes per turn to make decisions and give orders.[19]


During World War 1, the U-boats typically attacked convoys from outside the formation, striking ships at the perimeter. But reports from convoys in 1942 showed that U-boats were sinking ships at the center of the formation. Roberts surmised that the U-boats were somehow sneaking into the formation undetected before firing their torpedoes.[20] Roberts and his team tested various ways by which a U-boat might sneak into a convoy, sink a ship, and escape undetected. The only tactic that worked was for the U-boat to sneak into the convoy from behind, under the cover of night, at surface depth so that it could use its diesel engine to match the speed of the convoy, fire a torpedo at close range, then submerge and fall back.[21] Roberts and his team then developed a counter-tactic to defeat this. When a U-boat attack occurred, the escort ships were to reduce speed and fall back, forming a line behind the convoy. The escort ships were to then follow the convoy in a zig-zag pattern, listening for U-boats using sonar, and dropping depth charges when one was detected. This tactic was codenamed Raspberry (as in "blowing a raspberry at Hitler").[1]

Raspberry was in part disseminated by having naval officers come and participate in the wargames at WATU where they could experiment with Raspberry themselves. Raspberry was also published in the Western Approaches Convoy Instructions, a manual for escort ship captains. Soon enough, reports of successful U-boat sinkings, made possible by Raspberry, came in.

Beta Search[edit]

Beta Search was a tactic to be employed when an escort's lookout had sighted a U-boat. When a U-boat was spotted, the escort ship that spotted it was to move in its direction without firing flares, using sonar, or dropping depth charges. The U-boat's captain would reflexively order his ship to submerge. The escort ship was then to pass over it, making the U-boat crew believe they had escaped detection. The wargames predicted that the U-boat would then make a slow turn and assume a vector parallel to the convoy. At this point, the escort ships were to rush to the U-boat's predicted position. The rumble of the convoy's propellers would mask their approach. Once over the U-boat's predicted position, the escort ships were to release their depth charges.

Beta Search was jointly developed by Roberts and Laidlaw. It was so named because U-boat transmissions always began with a "B-bar" in Morse code (dash-dot-dot-dot-dash).[22] Admiral Horton personally tested Beta Search in a wargame at WATU. He played the role of the U-boat, while Janet Okell played the role of the escorts. Five times in a row, Okell sank Horton's U-boat.


  1. ^ a b Strong, Paul Edward. "Wargaming the Atlantic War: Captain Gilbert Roberts and the Wrens of the Western Approaches Tactical Unit" (PDF). paxsims.wordpress.com/. PAXsims. Retrieved 11 November 2019.
  2. ^ "Women winning battles: Recreating the Wrens unit which helped win the War". GOV.UK. UK Government. Retrieved 11 November 2019.
  3. ^ Overy (1995), Why the Allies Won. p. 31
  4. ^ Parkin (2019), A Game of Birds and Wolves. Ch 3: "‘Unless something was done in the Battle of the Atlantic,’ Roberts was told, ‘we were going to lose [the war], merely because vital food and war supplies would not arrive.’"
  5. ^ Parkin (2019), A Game of Birds and Wolves. Ch 8: "While the British could see from intercepted radio transmissions that U-boats were increasingly working together, providing the German vessels with safety in numbers, the specifics of their highly effective tactics could only be guessed at."
  6. ^ Parkin (2019), A Game of Birds and Wolves. Ch 8: "On the first day of 1942, Roberts was told to report to the Admiralty offices with an overnight bag. On arrival he met two of the navy’s most senior officers, the Second Sea Lord, Sir Charles Little, and Admiral Cecil Usborne, the former director of naval intelligence, now an aide to Winston Churchill. Usborne was responsible for overseeing the development of anti-U-boat weapons."
  7. ^ Parkin (2019), A Game of Birds and Wolves. Ch 8: "Churchill’s aide believed that Roberts, who had shown himself to be a talented strategist in Portsmouth and an enthusiastic proponent of games as a way to prepare for war, was the ideal person to evolve anti-U-boat tactics. Moreover, as a gifted communicator he was qualified to train escort commanders in those tactics."
  8. ^ a b Parkin (2019), A Game of Birds and Wolves. Postscript: "By 1945, a total of sixty-six Wrens had completed the course in order to become staff at WATU or its sister units."
  9. ^ Parkin (2019), A Game of Birds and Wolves. Ch 12: "Each course, which lasted from Monday to Saturday, and which ran weekly without interruption from the first week of February 1942 to the last week of July 1945, involved up to fifty officers at once."
  10. ^ Parkin (2019), A Game of Birds and Wolves. Ch 12, fn 1: "Roberts recorded that on Sundays the team would often be called upon to give demonstrations to visiting Americans."
  11. ^ Lindybeige (22 July 2018). The wargamers who won a real war (streaming video). Event occurs at 8m53s.
  12. ^ Hastings (2011), Inferno.
  13. ^ Parkin (2019), A Game of Birds and Wolves. Ch 10: "Roberts was to be given the entire top floor of Derby House, [...] comprising eight rooms."
  14. ^ Parkin (2019), A Game of Birds and Wolves. Ch 7: "In the autumn of 1937, he was appointed captain of the lithe destroyer Fearless [...] During these halcyon days, Roberts developed a wheezing, whistling cough that turned him into a sweating insomniac. [...] The doctor delivered his diagnosis on the spot: tuberculosis.
  15. ^ Parkin (2019), A Game of Birds and Wolves. Ch 7: "The progenitor of the wargame on which Roberts based his games in Portsmouth was Fred Jane [...] It was a version of the Jane Naval Wargame that Roberts adapted at his posting in Portsmouth"
  16. ^ Parkin (2019), A Game of Birds and Wolves. Ch 7: "Despite the fact that during the First World War the Germans had used submarines to great effect to disrupt the convoys bringing food and supplies to Great Britain, neither U-boats nor convoys featured in the wargames of 1935. [...] ‘Submarines were not mentioned,’ Roberts wrote of the games he was tasked with designing. ‘Nor were convoys and attacks on them. Nobody connected Hitler’s rise … to the possibility of another Battle of the Atlantic. Nor did I, to be absolutely fair.’"
  17. ^ Parkin (2019), A Game of Birds and Wolves. Ch 11: "The floor in the centre of the room was covered in brown linoleum, painted with white gridlines and punctuated with tiny wooden models [...] each white line was spaced ten inches apart, representing one nautical mile, while the counters represented ships and surfaced German U-boats.""
  18. ^ Parkin (2019), A Game of Birds and Wolves. Ch 11: "The movements of the U-boats were drawn in green chalk on the floor, a colour chosen as it was impossible to make out against the floor’s tint when viewed from an angle. This ensured the U-boat positions were undetectable to the players peering through the canvas screens. The escort ships’ movements would then be added to the floor in white chalk, which was, in contrast to the green markings, legible to those peeking from the canvas holes."
  19. ^ Parkin (2019), A Game of Birds and Wolves. Ch 11: "Players were given two minutes in which to submit their orders for the next ‘turn’, to replicate the urgency of a real battlefield."
  20. ^ Parkin (2019), A Game of Birds and Wolves. Ch 11: "If the U-boats were firing from outside the perimeter of the convoy, how had Annavore, which was in the centre of the convoy, been sunk? Might it be possible, he wondered, that the U-boat had attacked the ship from inside the columns of the convoy?"
  21. ^ Parkin (2019), A Game of Birds and Wolves. Ch 11: "Between them, Roberts and the two Wrens began to plot different scenarios that might have enabled the U-boat to sneak into the convoy without being detected. Only one checked out: the U-boat had entered the columns of the convoy from behind. And it must have done so on the surface, where it was able to travel at a faster speed than the ships. By approaching from astern, where the lookouts rarely checked, the U-boat would be able to slip inside the convoy undetected, fire at close range, then submerge in order to get away."
  22. ^ Parkin (2019), A Game of Birds and Wolves. Ch 13: "During the next few days Roberts and Laidlaw began to develop a replacement tactic [...] which they dubbed ‘Beta Search’, named after the fact that U-boat transmissions always began with the Morse B (Beta), or B-bar"


  • Max Hastings (2011). Inferno: The World at War, 1939-1945. Knopf Doubleday Publishing Group. ISBN 9780307957184.
  • Simon Parkin (2019). A Game of Birds and Wolves: The Secret Game that Won the War. Hodder & Staughton. ISBN 9781529353051.
  • Richard Overy (1995). Why the Allies Won. W. W. Norton & Company. ISBN 0-393-03925-0.