Japan’s wartime kamikaze pilots remain among the most recognisable symbols of the Pacific war: young men flying aircraft into Allied ships on missions from which they were not expected to return. Far less well-remembered are the fukuryu – suicide frogmen trained in the closing months of World War II to walk into the sea with mines on bamboo poles, then wait beneath the waves for an Allied invasion fleet. Kanade Hamamoto was one of many Japanese people who had never heard of them, despite...