Japanese submarine I-54 (1943)

The commander-in-chief of the Combined Fleet, Admiral Soemu Toyoda, activated Operation A-Go for the defense of the Mariana Islands on 13 June 1944.[1] The Marianas campaign began with the U.S. landings on Saipan on 15 June 1944.[1]

I-54 departed Yokosuka on 7 July 1944, bound for Saipan towing an Unpoto gun carrier,[1] a 70-foot (21.3 m) sled that could carry up to 15 tons of cargo, usually in the form of three Type 96 15-centimeter (5.9 in) howitzers and ammunition for them.[2] Fleet Radio Unit, Melbourne (FRUMEL), an Allied signals intelligence unit headquartered in Melbourne, Australia, intercepted and decrypted a Japanese message that day stating that I-54 was due to arrive at Tinian on 14 July 1944 to evacuate Imperial Japanese Navy Air Service personnel.[1] Saipan fell to American forces on 9 July 1944, and I-54 was ordered to nearby Tinian that day.[1] She lost her Unpoto sled in heavy seas.[1] On 10 July 1944, she was reassigned to Submarine Division 15 in the 6th Fleet.[1] On 15 July, FRUMEL intercepted and decrypted another Japanese message saying that I-54 was scheduled to arrive at Tinian on 18 July.[1] She returned to Yokosuka on 24 July 1944.[1]

Toyoda activated Operation Shō-Gō 1 for the defense of the Philippine Islands on 13 October 1944.[1] That day, I-54 was assigned along with the submarines I-26, I-45, I-53, and I-56 to Submarine Group A under the direct command of the 6th Fleet.[1] She departed Kure on 15 October 1944 with orders to attack the aircraft carriers of United States Navy Task Force 38 and the crippled light cruiser USS Houston (CL-81).[1]

On 18 October 1944, I-54 received orders from the 6th Fleet to join 12 other submarines in patrolling east of Leyte in the Philippines.[1] I-54 was assigned a patrol area 120 nautical miles (220 km; 140 mi) east of the Philippines between the areas assigned to the submarines I-38 and I-46, and she was expected to arrive in her patrol area on 25 October 1944.[1]

The Battle of Leyte began with the U.S. landings on Leyte on 20 October 1944, and that day I-54 acknowledged an order to change her patrol area. She transmitted another message on 23 October 1944, the first day of the Battle of Leyte Gulf of 23–26 October 1944.[1] The Japanese never heard from her again.[1]

The circumstances of I-54′s loss remain unknown.[1] At 12:18 on 28 October 1944, the destroyers USS Gridley (DD-380) and USS Helm (DD-388) detected a submarine attempting to penetrate the screen of United States Navy Task Group 38.4 — which included the aircraft carriers USS Enterprise (CV-6), USS Franklin (CV-13), USS Belleau Wood (CVL-24), and USS San Jacinto (CVL-30) — east of Leyte.[1][3] While the aircraft carriers steered away from the submarine contact at high speed, Gridley made three depth charge attacks against the submarine and Helm made four.[3] After Helm′s fourth attack, which took place at 14:11, a large explosion followed by two smaller ones occurred.[1][3] Oil and air bubbles appeared on the surface, and damaged deck planking and human remains were recovered after the attack.[3] The submarine sank at 10°58′N 127°13′E.[1][3]

On both 30 October and 1 November 1944, I-26, I-46, and I-54 all failed to make scheduled daily 19:00 status reports.[3] On 20 November 1944, the Imperial Japanese Navy declared I-54 to be presumed lost east of the Philippines with the loss of all 107 men on board.[1] She was stricken from the Navy list on 10 March 1945.[1]

The identity of the submarine Gridley and Helm sank remains a mystery, and has been reported both as I-46 and I-54.[1][3] Some sources have credited the destroyer escort USS Richard M. Rowell (DE-403) with sinking I-54 in the Philippine Sea on 26 October 1944 while screening Task Group 77.4, although the submarine Richard M. Rowell attacked probably was I-56, which survived.[1]