Shortly after the outbreak of the Second World War, a young Peter Calvocoressi was serving in the Ministry of Economic Warfare, his role largely consisting of reviewing shipping manifests day in day out. In 1940, he decided to volunteer for the War Office but was turned away on account of a recently-sustained head injury. The note on his file? "No good for anything – not even intelligence.” In spite of this, Calvocoressi was able to apply to the Air Ministry, was commissioned in RAF intelligence and, by early 1941, found himself at Bletchley Park.

Calvocoressi was assigned to a section of Bletchley dealing with Luftwaffe Ultra intelligence where – as deputy head and, from 1944, as head – he spent the rest of the war translating and interpreting decrypted Enigma signals.

The codebreaking operations at Bletchley Park came to an end in 1946, however all information about this wartime enterprise was classified and remained a secret until the mid-1970s, after which Calvocoressi recounted his experiences at Bletchley in Top Secret Ultra, published in 1980. This comprehensive new edition of Calvocoressi’s book features exciting new material from his son David and from renowned historian and author (specialising in signals intelligence) Dr Joel Greenberg. This is required reading for anybody with an interest in this utterly and indisputably fascinating aspect of the Allied war effort during World War II.