Primarily focuses on the Western Approaches Tactical Unit (WATU) school of anti-submarine warfare, which helped the allies turn the tide in the Battle of the Atlantic.

Also relays the story of founder Gilbert Roberts and the many Wrens who implemented the work and trained the Naval commanders. Chapters are short and to-the-point, with some photographs of the principals. The most detailed look into "war games" and their impact that I've read so far.

The book does wander a bit, and the reasons are not always plain at first. This includes the opening chapter, about children boarding a ship for America in the early days of the war. The sub-stories are also not strictly linear, which was a bit irritating. A solid 3½ stars.