His experiences as a cryptanalyst during World War II. U.S. Naval Academy, 1930-34. Qualities of a good cryptanalyst; Japanese language training in Tokyo, 1939-40; evacuation from Tokyo, August, 1941; assignment to HYPO, Pearl Harbor; impressions of Commander Joseph Rochefort; comments about Lieutenant Commander Thomas Dyer, Lieutenant Commander Joseph Finnegan, Lieutenant Wesley (“Ham”) Wright, Jasper Holmes; description of “The Dungeon” (Combat Intelligence Office); breaking of JN-25; relations between Rochefort and Fleet Intelligence Officer, Captain Edwin Layton; comments about “Magic” and “Winds Message”; evaluation of intelligence data; relations between HYPO and Office of Naval Intelligence; comments about Admiral Richmond Kelly Turner; Japanese attack at Pearl Harbor; Battle of the Coral Sea and Admiral Frank Jack Fletcher; comments about the Battle of Midway; off-duty activities; Rochefort’s transfer to CAST (Melbourne, Australia), November, 1943; Japanese withdrawal from Rabaul; ambush of Admiral Isoruko Yamamoto’s plane; return to HYPO; interrogation of Japanese POWs; H-bomb test at Eniwetok Atoll, 1952; retirement.