John Hattendorf was born in Hinsdale, Illinois on 22 December 1941, a fortnight after the Imperial Japanese Navy had flung the United States abruptly into the Second World War. The next few years were to contribute a great deal of naval history to the United States and the world, but few would have searched for a future naval historian in the outer suburbs of Chicago, nor in Gambier, the small town amidst the peaceful Ohio cornfields where John studied as an undergraduate at Kenyon College. But Kenyon, though far from the sea, was not isolated from the wider world, and certainly not from the scholarly world. Charles Ritcheson, the noted historian of the American Revolution, was then a professor at Kenyon. His experience included wartime service in the US Navy, and a DPhil at Oxford, while his private interests ranged from the Paris Opera to the Beefsteak Club. John also had close contact with the distinguished German medievalist Richard G. Salomon, driven from his chair in Hamburg in 1934, who retired from Kenyon in 1962 aged seventy-eight but remained an active scholar. At one period when he was housebound after a fall, John fetched books for him from the library: a new parcel every week, a book for every day, each in a different language. Salomon introduced John to the scholarly tradition of the Monumenta Germaniae Historica, and aroused in him an enthusiasm for archives highly unusual in an undergraduate. Over two years’ voluntary work, John listed and organised the college archives, and he edited A Dusty Path, an anthology of documents and photographs drawn from them. Salomon almost lured him into medieval church history – but not quite.

Instead, on leaving Kenyon in 1964, John joined the US Navy, and the following day, as he remembers, ‘someone started a war in a place called Viet Nam’. In February 1965 he was commissioned as an ensign, and before the end of the year he was at sea off that coast as an officer of the destroyer USS O'Brien. In 1967 he was mentioned in despatches for his ‘skill and judgement’ under fire. From the O'Brienhe went to the Naval History Division in Washington, where he found himself in danger of a different sort.