Type D submarine

The I-361 class submarine, also called Type-D submarine or Sen'yu/Sen'yu-Dai type submarine was a type of the 1st class submarine in the Imperial Japanese Navy serving during the Second World War. The type name, was shortened to Yusō Sensuikan Ō'-gata.
The I-373 class submarine, also called Type-D Modified submarine' was different from the I-361 class, however since the I-373 was a development form of the I-361 class, this article describes both of them.

Construction

After the Battle of Midway the IJN immediately planned a transport submarine. The type was based on the U 155 Deutschland. Her duties were transportation of troops in the areas where the enemy had air superiority. Later the demands for her were changed in sequence. The final demands were 65 tons in the hull and 25 tons on the upper deck. In the beginning the IJN did not intend to arm these boats with torpedoes. Later, after strong demands from the front commanders, it was decided to arm them with torpedoes for self-defense. The I-372 class was designed as a tanker submarine based on the I-361 class. They were not allowed to be loaded with torpedoes.

Service

In 1944, the submarines were tasked with transport missions between from mainland Japan to remote islands. They had little success and suffered great losses. Of the 13 submarines, only four survived the war.

Kaiten missions

In 1945, several submarines were converted to be Kaiten mother ships and assigned to the suicide attack operations for the Shinchō Tokubetsu Kōgekitai. Their deck guns were removed and fittings for five Kaitens were installed on their decks.

*Assigned to the Todoroki group on 24 May 1945, no success.
*Assigned to the Todoroki group on 28 May 1945, sank one motor ship on 15 June 1945.
*Assigned to the Tamon group on 8 August 1945, no success.
*Assigned to the Tamon group on 1 August 1945, no success.
*Assigned to the Shinbu group on 5 May 1945, damaged USS Gilligan on 27 May 1945.
*Assigned to the Tamon group on 19 July 1945, no success.
*Assigned to the Chihaya group on 20 February 1945, no success.
*Assigned to the Chihaya group on 20 February 1945, no success.

Class variants

The Type-D submarines were divided into four classes:Type-D/Sen'yuType-D/Sen'yu Mod.Type D Mod.Type D Mod.2/Type D 2 . The 2968th vessel class boats were not built and remained only a design.

''I-372'' class

Project number S51B. She was going to become a lead ship of the Modified Type D submarines, at first. However, the IJN wanted a submarine as soon as possible. She was built as a tanker submarine according to revised I-361 drawings.

Boat #	Name	Builder	Laid down	Launched	Completed	Fate
2961	I-372	Yokosuka Naval Arsenal	10 February 1944	22 June 1944	8 November 1944	Sunk by USN carrier aircraft from Task Force 38 at Yokosuka on 18 July 1945. I-372 was raised, towed to deep water, and scuttled in August 1946.

''I-373'' class

Project number S51C. Improved model of the I-361 class. Furthermore, the IJN was planned reinforced model of the I-373 class, also. However all of them were cancelled.

Boat #	Name	Builder	Laid down	Launched	Completed	Fate
2962	I-373	Yokosuka Naval Arsenal	15 August 1944	30 November 1944	14 April 1945	Converted to a tanker submarine in June 1945; sunk by USS Spikefish at East China Sea on 13 August 1945.
2963	I-374	Yokosuka Naval Arsenal	24 October 1944			Construction stopped on 17 April 1945, later scrapped.
2964	I-375					Cancelled on 17 April 1945.
2965 - 2967						Cancelled on 17 April 1945.