Kaichū type submarine

Class overview
Name	Kaichū type submarines
Builders	Kure Naval Arsenal Sasebo Naval Arsenal Yokosuka Naval Arsenal Kawasaki Shipbuilding Mitsui Engineering & Shipbuilding Mitsubishi Heavy Industries
Operators	Imperial Japanese Navy
Subclasses	Kaichū I (Ro-11 class) Kaichū II (Ro-13 class) Kaichū III (Ro-16 class) Kaichū IV (Ro-26 class) Toku-Chū/Kaichū V (Ro-29 class) Kaichū VI (Ro-33 class) Sen-Chū/Kaichū VII (Ro-35 class)
Built	1917-1944
In commission	1919-1945

The Kaichū type submarine (海中型潜水艦, Kaichū-gata sensuikan) submarines were double-hulled medium-sized submarines of the Imperial Japanese Navy during World War II. The name was derived from the Kaigun-shiki Chū-gata Sensuikan (海軍式中型潜水艦, Navy Medium Type submarine).

Several variants existed. From 1934 to 1944, the K6 type (Ro-33 Class) and the K7 type (Senchū, Ro-35 Class) were built. They were equipped with a 76.2 mm (3.00 in) L/40 gun and four 53 cm torpedo tubes for ten type 95 Long Lance torpedoes.

Most of these submarines were destroyed in combat, suffering from Allied anti-submarine warfare measures, and only Ro-50 survived the war.

The Kaichū type submarines were divided into seven classes:

• Kaichū I (海中1型（呂一一型）, Kaichū-ichi-gata, Ro-11-class)
• Kaichū II (海中2型（呂一三型）, Kaichū-ni-gata, Ro-13-class)
• Kaichū III (海中3型（呂一六型）, Kaichū-san-gata, Ro-16-class)
• Kaichū IV (海中4型（呂二六型）, Kaichū-yon-gata, Ro-26-class)
• Toku-Chū/Kaichū V (特中型/海中5型（呂二九型）, Toku-Chū-gata/Kaichū-go-gata, Ro-29-class)
• Kaichū VI (海中6型（呂三三型）, Kaichū-roku-gata, Ro-33-class)
• Sen-Chū/Kaichū VII (潜中型/海中7型（呂三五型）, Sen-Chū-gata/Kaichū-nana-gata, Ro-35-class)

Project number S7. In 1910s, the Imperial Japanese Navy (IJN) bought a license of Schneider-Laubeuf design submarine. The IJN used the design as model and built the S Type (Schneider Type) submarine, the Ha-9 and Ha-10. The Kaichū I is the submarine which jumboized the S Type submarines.

• Boats in class

Project number S18. The Kaichū II had an increased range compared with the Kaichū I, and the turning torpedo tubes were removed.

• Boats in class

Project number S18. Their project number was the same as in the Kaichū II type submarine, however their performance was improved.

• Boats in class

Project number S18A. Improved model from the Kaichū III type.

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Project number S18B. They were built for the commerce raiding role. The IJN official designation of these boats was Special Purpose-Medium Type submarine (特中型潜水艦, Toku-Chū-gata sensuikan).

• Boats in class

Project number S30. They were planned as a prototype for a mass production submarines in the wartime under the Maru 1 Programme.

• Boats in class

Project number S44. The final design in the Kaichū series. They were equipped with a Freon air-conditioner, because the IJN took into consideration that they were to be active on the equator area too. The official IJN designation of these boats was Medium Type submarine (中型潜水艦, Chū-gata sensuikan), also called for short, Medium Type (中型, Chū-gata) or Submarine-Medium Type (潜中型, Sen-Chū-gata).
The IJN planned to build these boats under the following Naval Armaments Supplement Programmes:

• 9 boats in the Maru Rin Programme (Boat # 201 - 209)
• 12 boats in the Maru Kyū Programme (Boat # 385 - 396)
• 15 boats in the Maru Tui Programme (Boat # 640 - 654)
• 43 boats in the Kai-Maru 5 Programme (Boat # 5181 - 5223)

However some of the boats were cancelled and their naval budgets, materials and staffs were transferred to the I-201 class submarines.

• Boats in class

• "Rekishi Gunzō"., History of Pacific War Vol.17 I-Gō Submarines, Gakken (Japan), January 1998, ISBN 4-05-601767-0
• Rekishi Gunzō, History of Pacific War Extra, "Perfect guide, The submarines of the Imperial Japanese Forces", Gakken (Japan), March 2005, ISBN 4-05-603890-2
• The Maru Special, Japanese Naval Vessels No.43 Japanese Submarines III, Ushio Shobō (Japan), September 1980, Book code 68343-44
• The Maru Special, Japanese Naval Vessels No.132 Japanese Submarines I "Revised edition", Ushio Shobō (Japan), February 1988, Book code 68344-36
• The Maru Special, Japanese Naval Vessels No.133 Japanese Submarines II "Revised edition", Ushio Shobō (Japan), March 1988, Book code 68344-37
• The Maru Special, Japanese Naval Vessels No.135 Japanese Submarines IV, Ushio Shobō (Japan), May 1988, Book code 68344-39