Ships
- IJN I-156 (I-156) Captain before mid-1942
- IJN RO-101 (RO-101) Captain, 31 October 1942 – 4 September 1943
- IJN I-177 (I-177) Captain, 6 September 1943 – 23 February 1944
- IJN I-47 (I-47) Captain from 10 July 1944 · Relieved in the spring of 1945
Zenji Orita left the Naval Academy at Etajima with the 59th class and went into submarines. On the morning of 21 November 1941 he was executive officer and torpedo officer of I-15, under Commander Nobuo Ishikawa. He was not her captain. Ishikawa told him they would sail that evening, and I-15 went out that night with the Advance Force for the attack on Pearl Harbor.
He already had command of the older submarine I-156 before the middle of 1942. On 20 July 1942 he was sent to fit out the new coastal boats RO-101 and RO-102. RO-101 commissioned under him on 31 October 1942. He was promoted lieutenant commander on 1 November.
In January 1943 RO-101 joined Submarine Squadron 7 at Rabaul. She covered the evacuation of Guadalcanal and patrolled east of Port Moresby. On 7 March 1943 she picked up Captain Kametaro Matsumoto and 44 soldiers from the wreck of Nojima Maru after the Bismarck Sea. Through the spring and summer she patrolled off Munda, Rendova, and the Kula Gulf, and PT boats usually kept her off the beach. On the night of 12 July she was on the surface charging batteries when Taylor attacked. His executive officer, Lieutenant Hiromi Tokugawa, and two lookouts were killed on the bridge. Orita cleared the bodies, shut the hatch, and took her down to about 460 feet. She then went to the northwest coast of Kolombangara to patch herself. On 18 August he fired four torpedoes at a destroyer off Horaniu. All four missed. He left her on 4 September 1943.
On 6 September he assumed command of I-177. He had her through the New Guinea supply runs and left her on 23 February 1944. His last boat was I-47, finished at Sasebo on 10 July 1944, and he was her first captain. That autumn she was fitted to carry four kaiten, torpedoes with a man inside and no way home. On 8 November she left Otsujima with I-36 and I-37. Before dawn on 20 November, about four and a half miles off Ulithi, he launched all four. One of them, believed to be Lieutenant (junior grade) Sekio Nishina's, hit the fleet oiler Mississinewa. She blew up at 5:47 a.m. Explosions in her 5-inch ammunition killed 63 men. It was the first successful kaiten attack of the war. I-47 was back at Kure on 30 November.
On 12 January 1945, off Hollandia, he launched four more. One damaged the Liberty ship Pontus H. Ross. On the way out he had taken eight starved soldiers off a raft 290 miles west of Guam. They had been adrift for 32 days. In late March, bound for Okinawa with six kaiten, Avengers bombed her. Two destroyers then hunted her for twelve hours east of Tanegashima. She survived 21 depth charges with a wrecked periscope and a fuel leak. A last patrol in late April and early May produced explosion reports he logged as hits. Most kaiten claims did not hold up afterward.
Japanese records relieve him on 25 April 1945, for Lieutenant Commander Masayoshi Suzuki. The boat's logs still have him at sea into early May, and then ashore, teaching tactics at the submarine school at Kure. Of the twelve men in his academy class who got their own boats, four lived. He was one of them. The Sixth Fleet promoted him as it disbanded in September 1945. In 1954 the new Maritime Self-Defense Force asked him back. He served until 1963, then went to a shipyard. In 1976 he published I-Boat Captain with Joseph D. Harrington.