The story of Navy Intelligence's OP-20-GZ as they helped to win the war in the Pacific by--once again--breaking the Japanese PURPLE code. Van Der Rhoer's father suggested to him that he skip the Romance languages and take up Japanese which was bound to be the most marketable language skill if the Japanese defeated China. So for five years he took lessons from a Buddhist priest in Manhattan. Come Pearl Harbor he was accepted by Navy Intelligence and sent to Washington where he gradually learned that the Navy had for years been in possession of the Japanese PURPLE code which was produced from a madly complicated typewriter derived from the German ENIGMA machine. Many of the messages that OP-20-GZ decoded could be understood when translated, but the famous order to bomb Pearl Harbor (""Climb Mount Niitaka"") meant nothing to them even then. Cryptanalysis was a weary business with moments of great excitement, especially when the first reports from Japanese vessels involved in the Battle of Midway began to come through. It was Van Der Rhoer's section which discovered that Admiral Yamamoto was making a secret flight past Guadalcanal and which helped set up the air ambush that killed the man who had planned and directed the attack on Pearl Harbor. The author follows the major battles of the South Pacific as they occurred and relates the feelings of the codebreakers, but it has almost all been done much more rousingly elsewhere. As in Ronald Clark's The Man Who Broke Purple (1977).