My father served in the Royal Navy during the second world war. He drank over-proof rum and smoked unfiltered cigarettes, both free of charge, while wearing a uniform that enhanced his natural attractions. What more could any teenager want? Of course, there were hazards in store when he set out from Liverpool. Worst of all was the weather. Atlantic storms could punch out portholes and bend iron stanchions. But a close second came U-boats, which sank ships in minutes.

The U-boats were dangerous not only for sailors. Their depredations almost cost Britain victory. By 1941, the losses of merchant vessels in the Battle of the Atlantic meant we faced starvation. The solution came from an unlikely source. Simon Parkin’s book is subtitled ‘the secret game that won the war’, because it was playing a game on dry land that helped turn the tide of hostilities at sea.

War games using boards and miniature pieces to simulate combat had been around since the 19th century, but hadn’t got far in the Navy. Indeed, the leader of its main war gaming unit in 1942 was not even a serving officer. Captain Gilbert Roberts was officially retired, invalided out of the Navy with tuberculosis. Moreover, most of his team were young women — very young women. They were ten Wrens, ranging in age from June Duncan, who was just 17, to the 21-year-old Jean Laidlaw. Yet as well as their youth and gender, they were distinguished by unusual brightness and enthusiasm.

The killer U-boat tactic was to slip into a convoy from behind, unseen by its escort of destroyers and corvettes. Once inside the convoy, merchant vessels were easy targets. To escape the escort the U-boats then dived and let the convoy pass overhead. Roberts and his team identified the ruse and produced a defensive stratagem. When a vessel was attacked, the escorts now trawled the area behind the convoy and depth-charged any U-boats detected there. The stratagem was known as ‘Raspberry’ — Laidlaw suggested the name, declaring they were blowing a ‘razz’ at Hitler.

The game used a giant grid, like a chessboard, set out on the floor in Derby House, the Navy’s Western Approaches HQ in Liverpool. As bombs showered down outside (Liverpool was a strikingly elegant city before the war), tiny vessels were moved around the grid. Chalk and string were vital adjuncts. Participants viewed the action through slits in canvas curtains to mimic distances visible at sea.

Once Raspberry’s effectiveness was proved, other new tactics followed. Senior officers were brought in for training sessions. Some of them were astonished at being coached by young women, but they got over it. One participant was a youthful Prince Philip. The Wrens were forbidden to speak to him but, as Parkin records, he was more charmer than curmudgeon. Soon enough the U-boats themselves faced annihilation.

Parkin is a journalist who writes regularly about computer games and he brings this background to bear here. His account covers catastrophic shipwrecks at length, as well as the other trials of seamen and civilians on both sides of the conflict. He could have given more space to additional factors that helped win the battle — in particular, advances in radar technology — and at times he loads unnecessary melodrama on to what is already a dramatic slice of history, but overall his treatment is engaging.

One highlight is his focus on the broader history of the Wrens, who made themselves indispensable to the Navy. Regrettably, while Roberts himself received awards and honours — though fewer than his due — the efforts of his Liverpool squad of wonder women went almost entirely unrecognised. Parkin himself deserves credit for bringing this little known episode back to life.