He was captain of the submarine I-58, which sank the American heavy cruiser USS Indianapolis in 1945 after its delivery of parts and enriched uranium for the first atomic weapon used in wartime, Little Boy, prior to the attack on Hiroshima.

After a number of unsuccessful operations, under the command of Hashimoto I-58 sank Indianapolis on 30 July with two Type 95 torpedoes while on a midnight patrol.

Hashimoto was called to testify on behalf of the prosecution at the court-martial of Charles B. McVay III, the commanding officer of Indianapolis, a move which was controversial at the time.

[1] Mochitsura Hashimoto was born in 1909 in Kyoto, Japan[2] the eighth of nine children and fifth son of a kannushi (Shinto priest).

The family did not have a naval background, but Hashimoto's father struggled financially on a priest's government subsidy and felt entering his son into the military would help to provide for them.

[14][15] On 15 July 1941, he was assigned to the submarine I-24, becoming its torpedo officer on 31 October, under Lieutenant Commander Hiroshi Hanabusa; the ship was based out of Kure.

[18] Hashimoto witnessed the final ritual of Kazuo Sakamaki and Kyoji Inagaki, who would man the midget submarine, which cast off at 05:30.

[18] For the remainder of 1942, Hashimoto operated his ship in home waters off Yokosuka training crews and trying new equipment and doing research for the development of Japanese submarine doctrine.

The submarine was later overhauled mid-construction to carry Kaiten manned torpedoes, which was considered a great honor by Hashimoto's crew.

She remained in port because of continued mining conducted by U.S. Army Air Forces, and departed on 16 July on another war patrol.

Hashimoto ordered the submarine to make for an area where he believed shipping lanes between Guam, Leyte, Peleliu and Okinawa intersected.

[33] At 23:35 that evening, Hashimoto spotted the heavy cruiser Indianapolis at 10,000 metres (33,000 ft) cruising for his position at medium speed.

[40] She picked up reports of the atomic bombing of Hiroshima in intercepted radio transmissions on 7 August but Hashimoto continued to hunt for Allied ships south of Bungo Strait.

I-58 surfaced in Bungo Strait on 15 August, where Hashimoto learned of the Gyokuon-hōsō signaling the Japanese surrender and end of the war.

[42] When Hashimoto came home from the war, he learned that his entire family had been killed in the atomic bombing of Hiroshima on 7 August.

Three days after Japan's formal surrender in Tokyo Bay, Hashimoto was promoted to his final rank of commander.

[43] On 20 November, he was given command of the destroyer Yukikaze, among the few Imperial Navy ships to survive the war, and assigned to repatriation duties, returning troops to Japan from overseas.

[44] Before Hashimoto could begin his new duties, however, he was summoned by the United States military to be a witness for the prosecution in the court-martial against Indianapolis commander Captain Charles B. McVay III, who was on trial on charges of negligence leading to the ship's sinking.

[45] For the duration of his time in the United States, he spoke through translator Francis Earl Eastlake from the Office of Naval Intelligence.

He spoke the next day with Captain John P. Cady, McVay's chief defense counsel, for several hours, as both officers sought to determine his credibility and competence to take the stand in the trial.

Following his appearance at the trial, Hashimoto remained in U.S. custody under guard until early 1946, when he was returned to Japan aboard USS Effingham.

Though Hashimoto was himself known to be innocent of any war crimes and was generally treated well by his guards, he spoke little English and was subject to derision in the press.

[53] Even after his departure his testimony remained controversial, and the Chicago Sun criticized his trip, which it estimated to have cost $1,820 (equivalent to $30,800 in 2023).

While penned up in his dormitory during the trial, he was treated more like an honored guest than an enemy officer who had caused the deaths of so many American boys.

"[57] In 1999, he assisted the surviving crew of the Indianapolis in attempting to exonerate McVay of blame for the ship's sinking, writing a letter to the Senate Armed Services Committee in which he stated, just as he had more than five decades earlier, that even if the Indianapolis had been zigzagging, there would have been no difference: "I would have been able to launch a successful torpedo attack against his ship whether it had been zigzagging or not."

[57]Hashimoto died at the age of 91 on 25 October 2000,[61] five days before a resolution to posthumously exonerate Captain McVay was passed by the U.S. Congress and signed by President Bill Clinton[citation needed].

When George W. Bush became president and Gordon England became secretary of the Navy, Secretary England directed Navy captain William J. Toti, former commanding officer of USS Indianapolis (SSN-697) to enter the exoneration language into McVay's service record in May 2001, finally closing this chapter of American naval history.