Use of outdated code led to ambush that killed Yamamoto, U.S. files show

WASHINGTON (Kyodo) The U.S. was able to decrypt secret Japanese communications that led to the death of Imperial Japanese Navy Admiral Isoroku Yamamoto during World War II because messages were still being written in an old cipher that should have been destroyed, according to declassified U.S. intelligence documents.

Although the U.S. military said after the war it was able to ambush Yamamoto after deciphering Japanese Navy messages, the specifics, such as what kind of messages, remained unknown.

Yamamoto, commander in chief of the Combined Fleet, was killed in an aerial ambush by U.S. Army Air Corps planes on April 18, 1943, while he was heading to Ballalae in the Northern Solomon Islands from Rabaul, the main base of Japanese military and naval activity in the South Pacific at the time.