Japanese submarine I-48

I-48 was the last of three Type C cruiser submarines of the C2 sub-class built for the Imperial Japanese Navy. Commissioned in September 1944, she operated as a kaiten manned suicide attack torpedo carrier during World War II and was sunk in January 1945.

Design and description
The Type C submarines were derived from the earlier KD6 sub-class of the Kaidai-class submarine with a heavier torpedo armament for long-range attacks. They displaced 2554 LT surfaced and 3561 LT submerged. The submarines were 109.3 m long, had a beam of 9.1 m and a draft of 5.3 m. They had a diving depth of 100 m.

For surface running, the boats were powered by two 6200 bhp diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 1000 hp electric motor. They could reach 23.6 kn on the surface and 8 kn underwater. On the surface, the C1s had a range of 14000 nmi at 16 kn; submerged, they had a range of 60 nmi at 3 kn.

The boats were armed with eight internal bow 53.3 cm torpedo tubes and carried a total of 20 torpedoes. They were also armed with a single 140 mm/40 deck gun and two single or twin mounts for 25 mm Type 96 anti-aircraft guns. They were equipped to carry one Type A midget submarine aft of the conning tower.

Construction and commissioning
Ordered under the Rapid Naval Armaments Supplement Programme and built by the Sasebo Naval Arsenal at Sasebo, Japan, I-48 was laid down on 19 June 1943 with the name Submarine No. 378. On 12 December 1943 she was numbered I-48 and Launched. She was completed and commissioned on 5 September 1944.

September 1944–January 1945
Upon commissioning, I-48 was attached to the Yokosuka Naval District and assigned to Submarine Squadron 11 in the 6th Fleet. She was configured to carry four kaiten manned suicide attack torpedoes on her after deck, two of them with access tubes that allowed their pilots to enter them while she was submerged. On 7 December 1944 she was reassigned to Submarine Division 15 in the 6th Fleet, and on 8 December she was assigned to the Kongo ("Steel") kaiten unit.

I-48 completed work-ups in the Seto Inland Sea on 26 December 1944 and proceeded to the naval base at Otsujima. She embarked her kaitens and their pilots there, and on 9 January 1945 became the last submarine of the Kongo unit to get underway for the U.S. naval base at Ulithi Atoll in the Caroline Islands to participate in a kaiten attack on the U.S. fleet there scheduled for 21 January 1945. The Japanese never heard from her again.

Loss
On 21 January 1945, I-48 was 18 nmi west of Ulithi Atoll proceeding toward the atoll on the surface at 18 kn when a Tinian-based PBM Mariner flying boat of U.S. Navy Patrol Bombing Squadron 20 (VPB-20) spotted her on radar at 19:30. When the plane tried to ascertain I-48′s nationality, she submerged, and the Mariner attacked her with two depth charges and a Mark 24 "Fido" acoustic homing torpedo. She survived, but aborted her kaiten attack on the anchorage.

After the Mariner′s crew reported the sighting, a hunter-killer group of three destroyer escorts — USS Corbesier (DE-438), USS Conklin (DE-439), and USS Raby (DE-698), with Conklin serving as flagship — from U.S. Navy Escort Division 65 began a search for I-48. The hunter-killer group′s commander made the assumption that I-48 was damaged and would head for Japanese-held Yap at an average submerged speed of 3 kn. After the group made no contact with I-48, the group expanded its search all the way to Yap on 22 January 1945.

At 03:10 on 23 January 1945, I-48 was on the surface 15 nmi northeast of Yap, proceeding southwest at 18 kn when Corbesier detected her on radar at a range of 9,800 yd. Corbesier closed the range and I-48 submerged. Corbesier picked up sonar contact on I-48 at 03:36 and fired a Hedgehog salvo that missed. Conklin and Raby also arrived on the scene. Corbesier fired five more Hedgehog salvoes without scoring any hits, then lost contact.

Corbesier regained contact on I-48 at 09:02 and fired another Hedgehog salvo, which missed. Corbesier again gained sound contact at 09:12, but lost it before she could attack again. Conklin, however, was able to launch a Hedgehog attack at 09:34 from a range of 550 yd. Seventeen seconds later, she heard four or five explosions at an estimated depth of 175 ft, followed at 09:36 by a violent explosion that knocked out Conklin′s engines and steering gear. Conklin observed huge air bubbles rising to the surface, soon followed by oil, wreckage, and large quantities of human remains. It marked the end of I-48, sunk with the loss of all 122 men aboard — her crew of 118 and four embarked kaiten pilots — at either 9.91667°N, 138.29167°W or 9.75°N, 138.33333°W, according to different sources. A motor whaleboat from Conklin later recovered pieces of planking, splintered wood, cork, interior woodwork with varnished surfaces, a sleeve of a knitted blue sweater containing human flesh, chopsticks, and a seaman's manual from the water 17 nmi north of Yap.

The Japanese 6th Fleet attempted to contact I-48 on 31 January 1945, ordering her to proceed to Kure, Japan. She did not acknowledge the order. She was stricken from the Navy list on 10 May 1945.