Kaichū type submarine

The Kaichū type submarine (海中型潜水艦) 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).

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 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 JAPANESE SUBMARINE Ro-50 survived the war.

Class variants
The Kaichū type submarines were divided into seven classes:
 * Kaichū I (海中1型（呂一一型）)
 * Kaichū II (海中2型（呂一三型）)
 * Kaichū III (海中3型（呂一六型）)
 * Kaichū IV (海中4型（呂二六型）)
 * Toku-Chū/Kaichū V (特中型/海中5型（呂二九型）)
 * Kaichū VI (海中6型（呂三三型）)
 * Sen-Chū/Kaichū VII (潜中型/海中7型（呂三五型）)

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 JAPANESE SUBMARINE Ha-9 and JAPANESE SUBMARINE 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.
 * Boats in class

Kaichū V (Toku-Chū, Ro-29 class)
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).
 * Boats in class

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.
 * Boats in class

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 submarine (中型潜水艦), also called for short, 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