Saw this on the History channel several weeks ago......
6 January 1946:
Arrives at Pearl Harbor. The I-400, I-401 and the I-14 are met by a Navy band and local celebrities.
18 February 1946:
Dry-docked at Pearl Harbor for evaluation.
26 March 1946:
Washington, DC. At a Submarine Officer's Conference, attended by former ComSubPac Vice Admiral Charles A. Lockwood, it is decided to dispose of all captured Japanese submarines by sinking.
4 June 1946:
The I-400 is a target ship in the Pacific off Pearl Harbor for tests of the Mark 10-3 exploder. At 1210, she sinks by the stern at 21-13N, 158-07W after being hit by three Mark 18-2 electric torpedoes fired by Cdr D. B. Bell's new USS TRUMPETFISH (SS-425).
ComSubPac, Rear Admiral Allan R. McCann (former CO of IOWA (BB-61), ComSubRon 5, Captain (later Vice Admiral) Elton W. Greenfell (former CO of GUDGEON (SS-211) and ComSubDiv 52, Cdr/MOH (later Vice Admiral) Lawson P. Ramage (former CO of PARCHE (SS-384) are embarked on the TRUMPETFISH and witness the I-400's sinking.