was an Imperial Japanese Navy Sentoku-type (or I-400-class) submarine commissioned in 1945 for service in World War II. Capable of carrying three two-seat Aichi M6A1 "Seiran" (Mountain Haze) float-equipped torpedo bombers, the Sentoku-class submarines were built to launch a surprise air strike against the Panama Canal. Until 1965, the Sentaku-type submarines — I-401 and her sister ships and — were the largest submarines ever commissioned.
Design and description
The I-400-class submarines had four diesel engines and carried enough fuel to circumnavigate the world one-and-a-half times. Measuring long overall, they displaced , more than double their typical American contemporaries. Until the commissioning of the United States Navy ballistic missile submarine in 1965, the I-400-class were the largest submarines ever commissioned.
The cross-section of the pressure hull had a unique figure-of-eight shape which afforded the strength and stability to support the weight of a large, cylindrical, watertight aircraft hangar, long and in diameter, located approximately amidships on the top deck. The conning tower was offset to port to allow the stowage of three Aichi M6A1 Seiran ("Clear Sky Storm") float-equipped torpedo bombers along the centerline. Aircraft were launched from a catapult on the forward deck forward of the hangar. A collapsible crane allowed the submarine to retrieve her floatplanes from the water.
In addition to the three floatplanes, each I-400-class submarine was armed with eight torpedo tubes, all in the bow, with 20 Type 95 torpedoes, a Type 11 deck gun aft of the hangar, three waterproofed Type 96 triple-mount antiaircraft guns mounted atop the hangar — one forward and two aft of the conning tower — and a single Type 96 25 mm antiaircraft gun mounted just aft of the bridge.
I-400-class submarines had a rather noisy special trim system that allowed them to loiter submerged and stationary while awaiting the return of their aircraft; demagnetization cables meant to protect against magnetic mines by nullifying the submarine′s magnetic field; an air search radar, two air/surface-search radar sets, and a radar warning receiver; and an anechoic coating intended to make detection of the submarine while submerged more difficult by absorbing or diffusing sonar pulses and dampening reverberations from the submarine's internal machinery.
Construction and commissioning
Ordered as Submarine No. 5232, I-401 was laid down on 26 April 1943 by the Sasebo Naval Arsenal at Sasebo, Japan. She was launched on 11 March 1944, and was completed and commissioned on 8 January 1945 with Lieutenant Commander Nobukiyo Nambu in command.
Service history
World War II
January–May 1945
Upon commissioning, I-401 was attached to the Kure Naval District and assigned to Submarine Division 1 — which also included her sister ship and the submarines and — in the 6th Fleet. She also was assigned to Submarine Squadron 11 for workups. The flagship of Submarine Division 1, she got underway from Sasebo on the day of her commissioning to begin workups in the western Seto Inland Sea with I-13 and I-400. She was at Kure, Japan, on 19 March 1945 when the United States Navy′s Task Force 58 launched the first Allied air strike against the Kure Naval Arsenal. More than 240 aircraft from the aircraft carriers , , , , , , and attacked Japanese ships in the harbor at Kure. American aircraft strafed I-401, but she was not damaged.
On 11 April 1945, I-401 put to sea from Kure with the commander of Submarine Division 1, Captain Tatsunosuke Ariizumi, embarked bound for Dairen, Manchukuo, where she was to load fuel oil for transportation back to Japan. I-401 ran aground shortly after leaving port, but freed herself and continued her voyage. On 12 April 1945, however, she detonated a mine laid by a United States Army Air Forces B-29 Superfortress in the Iyo Nada in the Seto Inland Sea northeast of the Himeshima lighthouse, bearing 037 degrees from the lighthouse. The explosion damaged some of her instruments and her aft ballast tank valves, forcing her to turn back to Kure for repairs. She underwent repairs during May 1945, and shipyard workers installed a snorkel aboard her while she was under repair.