Four boats were built in 1923-1929. Genealogy of the large-size submarine in the IJN began with U-142. Japan received six U-boats from Germany as reparations of World War I. The IJN copied U-125, one of the six, producing the I-21-class minelayer submarine. The IJN could not find an optimal design of fleet submarine, so they and Kawasaki Heavy Industries sent many technical officers to the United Kingdom and Germany and got drawings of advanced submarines. The British L class became the Kaidai I, the K class became the Kaidai II and U-142 become Junsen I.
Project number S32. This is a type which added a catapult to the Junsen I Mod. She was built in 1931 under the 1st Naval Armaments Supplement Programme (Maru 1).
Damaged aircraft carrier USS Saratoga 11 January 1942 Sank Clan Line cargo ship SS Clan Ross 2 April 1942 Sank RMS Bahadar 7 April 1942 Sank two unknown sailing boats 10 April 1942
Accidentally rammed, attacked and sunk by Toyokawa Maru northeast of Hachijo-Shima on 16 June 1944.
Junsen III (I-7 class)
I-7 in 1937
Project number S33. These boats combined the good points of the Junsen II and the Kaidai V. They were built in 1934 under the Maru 2 Programme.
Junsen III became a 'typeship' for the Type-A, B and C.
Sank Dutch merchant ship Tjisalak 26-03-1944 Sank RMS City of Adelaide 30-03-1944 Sank Australian merchant ship Nellore 29-06-1944 Sank USS Jean Nicolet 02-07-1944
Rekishi Gunzō, History of Pacific War Extra, "Perfect guide, The submarines of the Imperial Japanese Forces", Gakken (Japan), March 2005, ISBN4-05-603890-2
Model Art Extra No.537, Drawings of Imperial Japanese Naval Vessels Part-3, Model Art Co. Ltd. (Japan), May 1999, Book code 08734-5
The Maru Special, Japanese Naval Vessels No.31 Japanese Submarines I, Ushio Shobō (Japan), September 1979, Book code 68343-31
S: Single ship in classC: Converted to ship typeL: Officially classed as light cruisers until 1939 refitsI: Incomplete until the end of the warX: Cancelled
Japanese transcription: class/type (型, "Gata"), (re)model/mark (改, "Kai"), A (甲, "Kō"), B (乙, "Otsu"), C (丙, "Hei"), D (丁, "Tei")