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Intelligence Pertaining to the Loss of USS Indianapolis 

Links to Primary Source Pages 

Photocopies of the "Ultra" Extracts regarding the loss of USS Indianapolis are linked below.  The Intelligence Package is a collection of photocopies from documents in COMNAVSECGRU File 5830/114 on the Indianapolis investigation.  These were declassified by Executive Order 12356 on 18 May 1988.  The "Ultra" extracts show that intelligence existed that showed Indianapolis would travel through waters patrolled by Japanese submarines armed with Kaitens and standard torpedoes.  "Ultra" intelligence was closely guarded and had a very limited distribution, however.  It was authorized to be applied only when resulting action could bring material advantages in major strategic situations.  The USN could not risk distributing "Ultra" intelligence for action on lower level operations because the risk was too high that the Japanese would discover that their most sophisticated code was broken.  The transit of Indianapolis from Guam to Leyte to did not reach the strategic level for "Ultra" distribution.  The only non "Ultra" documents in the package, pp. 16-17, show the new operating procedures adopted by the Pacific Fleet following the loss of Indianapolis.

The Joint Intelligence Center Pacific Ocean Areas (JICPOA) Summations from the United States Navy File of SIGTOT Messages to CINCPAC Advanced Headquarters, shows a high level conversation between the offices of Captain Edwin T. Layton, intelligence officer CinCPac, John S. Harper, officer-in-charge, Fleet Radio Unit, Pacific  (FRUPac), and Captain Thomas H. Dyer, FRUPac's chief cryptoanalyst.  The messages show three of the Navy's most important crpytological officers attempting to figure out why Navy intelligence failed to recover the Japanese location of the Indianapolis attack. 

Published: Wed Dec 28 07:37:26 EST 2016