I-11 was an Imperial Japanese Navy Type A1 submarine that served during World War II. Designed as a submarine aircraft carrier and submarine squadron flagship, she was commissioned in 1942. She participated in the Guadalcanal campaign and patrolled off Australia, New Caledonia, and the Ellice Islands before she disappeared in 1944 during her sixth war patrol. She badly damaged the Royal Australian Navy light cruiser in 1943.

Design and description Type A1 submarines were versions of the preceding Type J3 with superior range and an improved aircraft installation, and they were fitted as squadron flagships. They displaced on the surface and submerged. The submarines were long and had a beam of and a draft of . They had a diving depth of .Bagnasco, p. 188

For surface running, Type A1 submarines were powered by two diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a electric motor. They could reach on the surfaceChesneau, p. 200 and underwater. On the surface, the Type A1s had a range of at ; submerged, they had a range of at .

Type A1 submarines were armed with four internal bow torpedo tubes and carried a total of 18 torpedoes. They were also armed with a single /40 deck gun and two twin Type 96 anti-aircraft guns.Carpenter & Dorr, p. 101

Unlike on the Type J3 submarines, the aircraft hangar was integrated into the conning tower and faced forward, and the aircraft catapult was forward of the hangar, while the deck gun was aft of the conning tower. Reversing the locations of the deck gun and catapult allowed aircraft launching from a Type A1 submarine to use the forward motion of the submarine to supplement the speed imparted by the catapult.

Construction and commissioning

Built by Kawasaki at Kobe, Japan, I-11 was laid down as Submarine No. 125 on 10 April 1939. Provisionally attached to the Kure Naval District on 5 February 1941, she was launched on 28 February 1941 and was named I-11 that day. She was completed and commissioned on 16 May 1942.

Service history May–July 1942 I-11 was formally attached to the Kure Naval District on the day of her commissioning, with Commander Tsuneo Shichiji in command, and also became the new flagship of Submarine Squadron 3 that day, replacing the damaged submarine in that role. She moved to Kure, Japan, in late May 1942 for work-ups, embarking an 11th Naval Air Arsenal Yokosuka E14Y1 floatplane for aircraft launch and recovery exercises.

I-11 departed Kure on 7 June 1942 and proceeded to Kwajalein Atoll, which she reached on 16 June. She continued her floatplane launch and recovery exercises at Kwajalein, during which one member of her crew suffered injuries due to an aircraft catapult malfunction. On 8 July 1942, she embarked the commander of Submarine Squadron 3, Rear Admiral Chimaki Kono, who transferred his flag from the submarine tender , as well as his six-man staff and a war correspondent from the newspaper Yomiuri Shimbun.

First war patrol

I-11 originally was scheduled to put to sea from Kwajalein in company with the submarine on 8 July 1942, but her departure was delayed until the day after, when she got underway to begin her first war patrol, assigned a patrol area in the Tasman Sea off the east coast of Australia. While on the surface there at 23:01 Australian Eastern Time on 20 July, she hit the Greek 5,482-gross register ton steamer with one torpedo off Jervis Bay, New South Wales, Australia. George S. Livanos, which was carrying a cargo of 87 military motor vehicles, sank seven minutes later. Still on the surface at 02:04 the next day, I-11 fired two torpedoes at the American 3,290-gross register ton armed merchant ship . Both torpedoes hit Coast Farmer amidships, and Coast Farmer sank 20 minutes later. illuminated Coast Farmer′s lifeboats after the sinking, and after examining them headed southwest along the Australian coast.

On 22 July at 05:45, I-11 was on the surface off the coast of New South Wales east of the lighthouse at Twofold Bay when she fired three torpedoes at the American armed Liberty ship , which was carrying a cargo of 82 jeeps, 72 half-ton pickup trucks, 60 one-ton trailers, and dozens of trucks, ambulances and halftracks. Two of the torpedoes hit, starting a fire, and William Dawes sank at approximately 16:30 with the loss of one United States Army soldier and four members of her United States Navy Armed Guard killed and four personnel wounded. That evening, an RAAF Bristol Beaufort torpedo bomber attacked unsuccessfully.

As I-11 continued to work her way to the southwest, her lookouts sighted what they reported as a convoy of eight transports escorted by two light cruisers and two destroyers at about 12:00 on 24 July. I-11 was unable to close with the ships because they were at a great distance. At 04:06 on the 27th, she fired a single torpedo at the Australian 2,197-gross register ton merchant ship Coolana while north of Cape Howe. The torpedo missed, so I-11 surfaced and attempted to attack Coolana with gunfire, but rough seas made targeting Coolana difficult with I-11′s deck gun. After Coolana transmitted an SOS, I-11 submerged and fired another torpedo, but it also missed, and Coolana escaped undamaged.

At 05:00 on 29 July, a Bristol Beaufort of the RAAF's No. 100 Squadron attacked I-11 when she was off Disaster Bay northeast of Gabo Island, and heading south at . I-11 made a crash dive and submerged before the Beaufort, whose bomb bay doors stuck, could drop its six bombs. The Beaufort's pilot claimed a kill, but I-11 was undamaged, although her crew found numerous bomb fragments on her afterdeck after she surfaced.

I-11′s lookouts sighted a convoy with several small escorts while she was on the surface in the Tasman Sea at 23:30 on 30 July 1942, and she set off in pursuit. At 02:50 on 31 July, southwest of the lighthouse at Cape Everard, she fired two torpedoes at overlapping targets and heard one explosion. The convoy's escorts attempted a counterattack, but could not locate I-11.

On 1 August 1942, I-11 reached the southernmost boundary of her patrol area at the eastern entrance to the Bass Strait and began her return voyage. She arrived at the Japanese naval base at Truk Atoll on 11 August 1942.

Second war patrol

While I-11 was at sea, the Guadalcanal campaign began with United States Marine Corps landings on Guadalcanal, Tulagi, Florida Island, Gavutu, and Tanambogo in the southeastern Solomon Islands on 7 August 1942. On 20 August, she began her second war patrol, departing Truk for a patrol area in the vicinity of the Santa Cruz Islands and southeastern Solomons. On 26 August, the commander of the Advance Force ordered I-11 and the submarines , , , , , , and to deploy to the south and east of San Cristobal to interdict American supplies and reinforcements bound for Guadalcanal. While in the Coral Sea southeast of Tulagi at 04:05 on 31 August, I-11 attacked what she identified as a 15,000-ton transport escorted by a destroyer and claimed two torpedo hits.

At 11:49 on 6 September 1942, I-11 was submerged northwest of Espiritu Santo in the New Hebrides at when she detected United States Navy Task Force 17, centered around the aircraft carrier and battleship . She penetrated the task force′s screen and identified Hornet as an "Enterprise-class" aircraft carrier. As Hornet passed ahead of her at 12:49 at a range of , I-11 fired four torpedoes, dived to , and rigged for silent running.

At 12:51, Hornet sighted a torpedo wake off her starboard quarter, and the pilot of a TBF-1 Avenger torpedo bomber patrolling overhead saw what he identified as the conning tower of a submarine breaking the surface between North Carolina and a destroyer on plane guard duty. The Avenger pilot dropped a depth charge on what he thought was a conning tower; its explosion detonated two of I-11′s incoming torpedoes, and I-11′s crew heard two large explosions at 12:52. Hornet began a hard turn to port, while North Carolina turned to starboard. One torpedo passed off North Carolina′s port side.

The task force's escorts began searching for I-11, and at 14:52 the destroyer gained contact on her and dropped six depth charges. At 15:13, Russell′s lookouts sighted an oil slick long by 0.5 nautical mile (0.9 km; 0.6 mi) wide, but Russell lost contact with I-11 at a range of . When Russell regained contact, I-11, operating at a depth of , made a late detection of the approaching destroyer and commenced a dive to . Russell′s subsequent depth-charge attack resulted in a number of explosions close aboard that caused a minor leak at I-11′s stern through her propeller shaft gland, temporarily disabled her sound gear, and wrecked 80 per cent of her batteries. The battery damage and leak caused her forward compartments to fill with poisonous chlorine gas. I-11 reached a depth of before her crew could regain control of her.

I-11′s crew put on gas masks and rewired the intact batteries to partially restore electrical power. During the evening of 6 September 1942, seven hours after the depth-charge attack, I-11 surfaced. Her crew assessed that they could repair the leak, but determined that I-11 could not dive, so she made for Truk on the surface at best possible speed. On 7 September 1942, a U.S. Navy PBY-5 Catalina flying boat of Patrol Squadron 11 (VP-11) attacked her northeast of Santa Isabel Island at while I-11′s crew fired at the PBY with her deck gun and her four 25 mm antiaircraft guns, along with three Type 38 carbines and her floatplane's 7.7 mm (0.303 in) Type 92 machine gun, which they had lashed to her bridge railing. The PBY dropped three bombs, one of which landed close aboard but inflicted no further damage. Another PBY attacked her on 8 September 1942 between 14:00 and 14:15, making several strafing runs and scoring another near-miss with a bomb. She reached Truk on 11 September 1942.

September 1942–January 1943

At Truk, Submarine Squadron 3's flag shifted from I-11 to the submarine tender Yasukuni Maru and makeshift repairs were made on I-11. With them complete, she departed Truk on 15 September 1942 and headed for Kure, making the entire voyage on the surface. She reached Kure on 23 September 1942, returned her floatplane — which had survived Russell′s depth-charging in flyable condition — to the 11th Naval Air Arsenal, and began repairs. After completion of her repairs, I-11 departed Kure on 9 January 1943 and arrived on 15 January at Truk, where on 18 January she was designated the flagship of Submarine Force A under the command of Rear Admiral Katsumi Komazawa.

Third war patrol

The Japanese decided in January 1943 to evacuate their forces from Guadalcanal in Operation Ke. With a Yokosuka E14Y (Allied reporting name "Glen") floatplane aboard, I-11 departed Truk on 19 January to begin her third war patrol, resuming her participation in the Guadalcanal campaign. She was assigned a patrol area south of Guadalcanal and north of Rennell Island, where she and the submarines , , , , , , , and were tasked to intercept Allied naval forces steaming to and from the Guadalcanal area.

On 31 January, I-11 received orders to proceed to the waters east of San Cristóbal in support of ships of the 2nd and 3rd Fleets as they conducted the evacuation. On 2 February 1943, Rear Admiral Komazawa ordered the submarines of Submarine Squadron 3 to intercept a U.S. Navy aircraft carrier task force reportedly operating southeast of San Cristóbal. At 10:00 on 7 February, I-11 sighted a U.S. aircraft carrier steaming south and began an approach, but an inaccurate depth setting for I-11′s torpedoes prevented a successful attack. The Japanese completed the evacuation of Guadalcanal on 8 February 1943.