The Junsen type submarines were divided into four subtypes: • • • • .
Junsen I (I-1 class) Four boats were built in 1923-1929. Genealogy of the large-size submarine in the IJN began with . Japan received six
U-boats from Germany as
reparations of
World War I. The IJN copied , 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 became Junsen I.
Junsen I Mod (I-5 class) This is a type which added a
floatplane to the Junsen I.
Junsen II (I-6 class) 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).
Junsen III (I-7 class) 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. ==Characteristics==