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U-Boat Wargamers

The story of the U-Boat Wargamers 

Image: U-Boat Wargamers

U-Boat Wargamers tells the story of the Women's Royal Naval Service (WRNS) who helped take down Germany's fearsome U-boats.

The Battle of the Atlantic was one of the most important battles during the Second World War. Britain’s survival depended on the vital supplies being shipped from the United States, but the growing menace of Hitler’s U-boats threatened to cut them off.

If those supplies dried up, Britain’s defeat in the war was inevitable. As Churchill once wrote, ‘... the only thing that ever really frightened me during the war was the U-boat peril.’ The tactics of the German submarines needed to be understood, unpicked and outsmarted. The answer lay not on the battlefield but on a board game played with chalk, string and wooden figurines.

The wargame was conducted and carried out by a group of select ‘Wrens’ (members of the Women’s Royal Naval Service) and a discharged navy captain.

Here’s how they used it to tip the Battle of the Atlantic in the Allies' favour.


The Nazi conquest of France and Norway had given Germany forward operating bases from which they could launch their U-boats into the Atlantic. Between June 1940 and the end of the year, U-boats sunk three million tons of Allied shipping.

The commander of the U-boats, Admiral Karl Dönitz, had developed strategies, including the ‘Wolf Pack’ attack tactic, that were wreaking havoc on Allied supplies in the Atlantic. Something had to be done before Britain was starved into submission.

Gilbert Roberts

At the tender age of twelve, Gilbert Roberts joined the Royal Navy. During the mid-1930s, he studied at Portsmouth Tactical School where he was first introduced to the art of naval wargaming; something he quickly took to.

However, his career came to an early end in 1938 after suffering from a bout of tuberculosis. Deemed medically unfit, Roberts retired from the Navy.

However, on 1st January 1942, he found himself with purpose once again after being summoned to report to the Western Approaches HQ in Liverpool. There he was tasked with establishing the Western Approaches Tactical Unit (WATU) to put his wargaming skills to good use by deciphering and combating Karl Dönitz’s U-boat tactics.

The Wrens

Accompanying Roberts in his task was a select group of Wrens chosen for their mathematical and statistical capabilities. Among them were 19-year-old Janet Okell and 21-year-old chartered accountant Jean Laidlaw. Both women played a pivotal role in subduing the U-boat peril.

Derby House

Known by staff as 'The Citadel', Derby House in Liverpool was the secret command centre from which Britain waged its war in the Atlantic. Roberts and the Wrens were given the entire top floor of Derby House to stage their wargames.

The team got straight to work converting the lino-clad floor into a giant board game, divided with painted sectors and marked by string and chalk. With the help of eyewitness testimony and gathered intelligence, the Wrens designed a game that allowed them to stage battles as accurately as possible.

The gridlines were measured to represent nautical miles and escort ships, and U-boats became tiny wooden models with different coloured chalk displaying their movements.

One team would play as the U-boats, the other as the escort ships. The U-boat players had full visibility of the board, whilst the ship commanders had to sporadically peer through holes in a canvas screen to recreate the limited visibility at sea.

Each team was allowed just two minutes to make their move and Wrens moved around constantly, relaying information to act as radio chatter. The pressurised conditions of the game became the perfect training ground for naval officers and it wasn’t long before week-long courses were being conducted on the top floor of The Citadel.

Dönitz outsmarted

Sceptics of WATU were soon eating humble pie after the Wrens successfully discovered the secret of Dönitz’s tactics.

One night Roberts, Okell and Laidlaw were playing the game and testing out different scenarios. Reports had been flooding in that merchant vessels were being sunk at the centre of Allied convoy formations, with no sign of U-boats anywhere. How was this possible?

The conventional belief was that the U-boats were firing between the escort ships and hitting their target from a distance. But what if they were much closer than previously believed? The team decided to test this theory and placed a U-boat within the convoy and set about working out how it got there, why it wasn’t detected and how it left.

After playing the game multiple times, there was only one answer that made sense. The U-boats snuck up behind the convoy - where look-outs on the ships rarely checked - at night and above the surface. This not only gave them the element of surprise but also the speed to catch up with the ships. Once inside the formation, the U-boat became indistinguishable from the other ships on the radar.

Shooting at a closer range was also much easier and helped explain the high success rate the U-boats were having. The submarines would then slip away by diving underwater, allowing the convoy to pass overhead. All of this explained how the U-boats seemingly struck from nowhere and disappeared just as easily.


After this revelation, the team reset the game and played it with the mindset of countering this newly discovered U-boat tactic. They came up with a triangular sweeping manoeuvre that allowed the Royal Navy escort ships to better target the position of the hidden U-boat.

Laidlaw dubbed the countermeasure ‘Raspberry’, as in a razz of contempt aimed at Hitler and his U-boats. The revolutionary tactic was seized upon by the Royal Navy high command who passed it on to all officers at sea. By mid-1942, Allied vessels began sinking U-boats in numbers previously unseen, all thanks to the ingenuity of the tactics developed by the Wrens.

The Wrens continued to use the wargame to develop more manoeuvres to counter Wolf Pack formations as well as other U-boat scenarios. Each new tactic was named after a fruit or vegetable.

Dönitz defeated

By May 1943, Dönitz had realised the time of the U-boat had passed and he ordered their withdrawal from the Atlantic. The Wrens had proven to be his nemesis. After Germany had fallen in 1945, Roberts visited the German U-boat HQ in Flensburg. There he saw a portrait of himself on the wall with the accompanying caption, ‘This is your enemy’.

By the time WATU officially closed in 1945, over 5,000 naval officers had been trained by the Wrens and cut their teeth on the wargame developed at Derby House. A total of 66 Wrens served at WATU between 1942 and 1945, each one making an immeasurable contribution to the Allied war effort.