Kaichū type submarine

The Kaichū type (海中型) submarines were double-hulled medium sized submarines of the Imperial Japanese Navy during World War II. They were derived from the Kaigun-shiki Chūgata Sensuikan (海軍式中型潜水艦).

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 3.0 inch (76.2 mm) 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 the Ro-50 survived the war.

Class variants
The Kaichūs were divided into seven types; Kaichū I - VII

Kaichū I (Ro-11 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

Kaichū II (Ro-13 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

Kaichū III (Ro-16 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

Kaichū IV (Ro-26 class)
Project number S18A. Improved model from the Kaichū III type.
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Kaichū V (Toku-Chū, Ro-29 class)
Project number S18B. They were built for economic-warfare role. The IJN official designation of these boats was Special Purpose-Medium Type (特中型).
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Kaichū VI (Ro-33 class)
Project number S30. They were planned as a prototype for a mass production submarines in the wartime under the Maru 1 Programme.
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Kaichū VII (Sen-Chū, Ro-35 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 (中型) or Submarine-Medium Type (潜中型).

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