21:00 on 18 August 1945, Ariizumi aboard I-401 received orders from the 6th Fleet to cancel the Ulithi attack, and later that day I-400 and I-401 were ordered to proceed to Kure. End of war On 26 August 1945, I-400 received orders to hoist a black flag of surrender and to disarm herself. Accordingly, her crew assembled all three of her M6A1 aircraft and catapulted them unmanned into the sea, dumped their bombs overboard, fired all of her torpedoes, and destroyed all of her logs, charts, codebooks, and secret documents. I-400 was in the Pacific Ocean east of Honshu on 27 August 1945 when an aircraft from U.S. Navy Task Force 38 sighted her at . The destroyers and intercepted her, and she surrendered to them northeast of Tokyo. The same day, a U.S. Navy prize crew of four officers and 40 enlisted men from the submarine tender set out aboard the destroyer escort to take charge of I-400. Weaver arrived alongside I-400 on 28 August 1945 and put the prize crew aboard her, and I-400 headed for Japan under command of the prize crew, escorted by Blue and Weaver. At 09:15 on 29 August 1945, she arrived in Sagami Bay on the coast of Honshu and moored alongside Proteus′s port side. At 09:55, I-14 also arrived under the command of a U.S. Navy prize crew, and she moored alongside I-400′s port side. At 08:20 on 30 August 1945, I-400 got underway in company with I-14 and Proteus bound for Tokyo Bay, where they anchored at 14:58 the same day. The United States flag was raised aboard her at 05:00 on 31 August 1945, and at 14:45 I-400, I-14, and Proteus began a move to a new anchorage within the breakwater at the submarine base at Yokosuka, where Proteus was anchored by 16:50. Twelve U.S. Navy submarines chosen to represent the U.S. Navy Submarine Force at the Japanese surrender ceremony in Tokyo Bay also were anchored there, and I-401 arrived on 31 August as well. During the surrender ceremony on 2 September 1945, the Commander, Submarine Force, U.S. Pacific Fleet (COMSUBPAC), Vice Admiral Charles A. Lockwood, ordered his personal flag hoisted aboard I-400 and I-401. Postwar The Japanese struck I-400 from the Navy list on 15 September 1945. On 29 October 1945, I-401 got underway from Yokosuka southbound for Sasebo with a 40-man American crew aboard in company with I-401,