Ki-3 Class Submarine:
Developement of a successor class for the Ki-1 class was in planning stage since early 1922, but developement was halted until the first of the Ki-1 units completed it's sea trails, so that the program was not finalized until early 1925. For the new class, Koko no Kaigun Naval Staff ultimately opted for a modified L4 Type units (whose design was nothing more than a license copy of the British third batch of L-Class submarines), the hullw as lenghtened slightly in order to fit more powerful engines for a top speed of 16 knots surfaced and 9 knots submerged. The units displaced 1.016T standard and 1.359T submerged. Other specification were the same as the japanese counterparts: six 533mm torpedo tubes at the bow and a 76mm/40 anti-aicraft gun, endurance of 5.500 nutical miels surfaced (at 10 knots) and 80 miles submerged (at 4 knots). Test depth was 60 meters and crew complemement amounted to 48 men.
Eight units, named and numbered Ki-3 through Ki-10, were ordered at Kumoi Arsenal by mid 1925. The lead ship was laid down by the end of the year, with the others following by 1928. One unit, Ki-9, was reordered on a larger design and built at Toumachi Naval Arsenal. The seven remaining ships were commissioned between 1929 and 1931, forming two Sensuitai.
During the Pacific War all units operated closer to home waters as the the later, larger submarines were deemed more capable. Ki-6 was lost in Aleutian waters, with the other units sunk between 1945 and 1946. Only Ki-5 survived the war, just to be immediately taken out of service and scrapped.
Ships in class: (laid down-launched-commissioned - fate)
Ki-3 1925-1927-1929 - Sunk 1945
Ki-4 1926-1927-1929 - Sunk 1946
Ki-5 1926-1928-1929 - Decommissioned 1946
Ki-6 1926-1928-1929 - Sunk 1943
Ki-7 1927-1929-1931 - Sunk 1946
Ki-8 1927-1929-1930 - Sunk 1946
Ki-10 1928-1930-1931 - Sunk 1945