Western Approaches Tactical Unit


The Western Approaches Tactical Unit 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. It was led by Captain Gilbert Roberts and was principally staffed by officers and ratings from the Women's Royal Naval Service. Their primary tool for studying U-boat attacks and developing countermeasures was wargames. After the U-boat threat to merchant shipping was defeated, WATU continued to develop anti-submarine tactics for later stages of the war, including Operation Overlord and the Pacific War. WATU trained naval officers in its tactics by hosting week-long training courses in which the students played wargames. WATU formally ceased operations at the end of July 1945, about two weeks before World War 2 ended with the surrender of Japan.

Mission

During World War 1, 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 which were escorted by warships armed with depth charges. This strategy 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, exploiting the weaknesses of the convoy system, and new advances in submarine technology. The British, by contrast, had neglected to study submarine tactics during the inter-war years. They entered World War 2 assuming that the U-boats 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, Germany sent its U-boats to attack transatlantic 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. 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. 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. 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. 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.
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, and likewise Roberts recruited most of his staff from the Wrens. At total of sixty-six Wrens served at WATU from 1942 to 1945.
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. 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. 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, 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.
In May 1943, Admiral Karl Doenitz ordered the U-boats to withdraw from the Atlantic, allowing merchant convoys to pass unmolested. In 1944, food imports to Britain rose to 56.9 million tons.
WATU continued to develop anti-submarine tactics and train officers until the end of the war. It officially ceased operations at the end of July 1945. It had trained close to 5,000 officers over its lifetime.

Legacy

What makes WATU a noteworthy 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.

Headquarters

was an operational command of Britain's Royal Navy, tasked with safeguarding British shipping in the Western Approaches. 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 the headquarters is a museum. The top floor, comprising eight rooms, was allocated to WATU. 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

A total of sixty-six women from the Women's Royal Naval Service served at WATU from 1942 to 1945.

Staff

Overview of the wargames

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. 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.
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. 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.
The players were given two minutes per turn to make decisions and give orders. The players issued their orders for their imaginary ships on pieces of paper that they passed to the Wrens—this prevented their opponents on the other side of the room from overhearing. The Wrens would then get down on the floor and compute the outcomes of the players' orders. Roberts provided the Wrens with the performance characteristics of all ships concerned: the range of the U-boat's torpedoes, the speed of the ships, their turn speed, the precise capabilities of the escorts' sonar, how engine noise might distort listening attempts, visibility at night, etc. The Wrens would plot the trajectories of the ships on the game board with chalk.

Tactics developed

''Raspberry''

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. Roberts and his team tested various ways by which a U-boat might sneak into a convoy, sink a ship, and escape undetected. Only one tactic worked on the game board: The U-boat snuck into the convoy from astern at surface depth so that it could use its diesel engine to match the speed of the convoy. Since these attacks happened at night, the U-boat was not easily spotted by look-outs, and once inside the convoy it was indistinguishable on radar and sonar. The U-boat would then sink a merchant ship with a torpedo at close range, then submerge and turn around to make its escape from astern.
Roberts and his team then developed a counter-tactic to defeat this. When a merchant ship in the convoy was torpedoed, the escort ships to the rear and flanks were to fall back and form a tight line behind the convoy. The line of escort ships was to then trawl for the U-boat using sonar, and drop depth charges when the U-boat was found. The escorts in front of the convoy were to stay ahead and move in a zig-zag patten in case the U-boat tried to escape from the front at full speed. At the suggestion of Jean Laidlaw, this tactic was codenamed Raspberry, as in "blowing a raspberry at Hitler".
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.

''Pineapple''

Pineapple was meant to be used when a possible U-boat was detected somewhere far ahead of the convoy—perhaps by reconnaissance planes, radio direction finders, or intelligence reports—but which hadn't yet been sighted by the escorts' look-outs. Ever since Raspberry was deployed, Roberts had been concerned that eventually the German navy would figure out how Raspberry was sinking their U-boats and alter their tactics. Perhaps a U-boat ahead of the convoy might observe Raspberry in action and report what it had seen to German naval command—this scenario was the impetus for developing Pineapple. The basic outline of this tactic was proposed by a visiting officer from the Canadian Navy. The diagram he drew for Roberts somewhat resembled a pineapple, so that's what Roberts called it.
The basic idea of this tactic was to trick the U-boat into an encirclement where it could be sunk, or at least scare it off. Either was better than letting it lurk near the convoy where it might observe Raspberry in action or launch an attack of its own. When a possible U-boat was detected ahead of the convoy, the escort ships at the front and the flanks of the convoy were to advance at full speed for 15 minutes, firing star shells along the way to light up the surface of the water. This would prompt the U-boat to submerge if it wasn't already. While the escort ships moved at full speed, their sonar was useless because of the noise, so the U-boat was safe from detection at this point. The U-boat might now choose to slip away and attack another night, or it might press on towards the convoy, resurfacing after the escort ships passed by. After completing their 15-minute sortie, the escort ships were to turn around and slowly return to their normal positions around the convoy, all the while scanning the water with sonar. If the U-boat was still around, it would be detected in this sweep and attacked.

''Beta Search''

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. 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.

''Step-Aside''

Step-Aside was a tactic by which an escort ship could defend itself from a U-boat armed with acoustic torpedoes, specifically the T5 Zaunkönig torpedo, which the German navy began using in August 1943. This torpedo used built-in hydrophones to guide itself to its target by sound.
In late 1943, Roberts received reports that the U-boats were regularly targeting the escort ships themselves. Stripped of their escorts, the merchant ships became easy prey. There was a common pattern in these reports: The escort ship would sight a U-boat and head straight for it, but then the escort ship would somehow get hit in the stern. This was a puzzling pattern. In those days it was very difficult for a submarine to torpedo a ship that was heading straight for it. From that angle, the ship had a narrow profile and with a slight turn it could easily dodge a conventional torpedo. U-boats preferred to attack ships from the side at an angle on the bow of 45 to 90 degrees. Furthermore, a conventional torpedo should have hit the escort ship in the bow because it was headed straight at the U-boat. A mine was suggested to be the mystery weapon but that was unlikely given how often this pattern repeated. Roberts surmised that the Germans were using a new type of torpedo that could guide itself to its target by following the sound of the target's propeller. Such a weapon had long been dreamed of by submariners and Roberts deduced that the Germans had just invented the first practical one.
Roberts surmised that the Germans' acoustic torpedo could only track targets that were in a 60 degree arc ahead of it, so the escort ship must first place itself outside this arc when it went after the U-boat. When the escort ship sighted a U-boat, it was to turn towards the U-boat and fire a star shell to let the U-boat know that it had been spotted, which would prompt the U-boat to submerge and fire its acoustic torpedo. The escort ship was to then turn 150 degrees away from the convoy and sail for one mile at a speed of 15 knots. The escort ship was to then turn onto the bearing on which it initially spotted the U-boat, which would put it on a course roughly parallel to the torpedo. After another mile, it was to turn towards the U-boat's last known location, locate it with sonar, and drop depth charges.
As soon as it was completed, Step-Aside was communicated by radio to escort commanders at sea on 23 September 1943. Thanks in part to Step-Aside, the Germans' acoustic torpedo never achieved its full destructive potential. The Allies also used decoy sound generators such as "Foxer" and CAT to counter the acoustic torpedo.

Footnotes