The Kaidai class was a class of submarines operated by the Imperial Japanese Navy before and during World War II. All Kaidai class submarines originally had a two digit hull number, from I-51 onwards. In 1942, many of the active units of the class had a 1 prefixed to their designation. For example, I-52 became I-152. Ships will be listed by the three digit hull number if they had one, two digit if they were not granted one or left service before 1942.

Class variants

Kaidais were divided into seven types; KD1 - 7

KD1

The prototype for the class. The sole KD1, I-51, was based on World War I-era German submarines. She was completed in 1924, was refitted with new engines in 1932, and was scrapped in 1941. I-51 never saw combat. ^[1]

KD2

There was only 1 KD2, I-152. She was completed in 1929, used as a training vessel until mid-1942, then struck from service. She was scrapped in 1946. There were to be six KD2s, but the latter 5 were cancelled. ^[2]

KD3

The nine KD3s were based on earlier designs, but featured a strengthened hull. There were two sub-types; KD3A (I-53, I-54, I-55, and I-158) and KD3B (I-156, I-157, I-159, I-60, and I-63). The "B" types were 40 cm longer, and had a different bow design. All nine ships were constructed between 1927 and 1930. ^[3]

Of the nine KD3s, seven survived the war, as they spent much of their time as training vessels. These were scuttled or scrapped shortly after the end of World War II. I-63 was sunk in a collision with I-60 in 1939, the former losing all crew. I-63 was refloated and scrapped in 1940. I-60 was later sunk by HMS Jupiter. ^[3]

KD4

Slightly smaller than her predecessors and with only four torpedo tubes, three KD4s were constructed between 1929 and 1930; I-61, I-162, and I-164. I-61 was lost in a collison in 1941. I-162 was sunk by USS Triton on 17 May 1942. I-161 survived the war. ^[4]

KD5

3 KD5s were constructed; I-165, I-166, and I-67 were all completed in 1932. The design saw the upgrade of the deck weapon from a 50 cal to a 65 cal dual-purpose gun. The submarine was also slightly wider and taller, with an increased crew complement of 75 and an increased maximum depth of 230 ft (70 m). I-165 was modified in 1945; her gun removed and two Kaiten midget submarines/manned torpedoes. ^[5]

None of the KD5s survived World War II. I-67 was lost with all 87 crew during an exercise in 1940. I-165 was sunk on 27 June 1945, off the east coast of Saipan. I-166 was sunk by British submarine HMS Telemachus on 17 July 1944, off the coast of Singapore. ^[5]

KD6

Constructed over the course of 1934-1938, eight KD6s were built; I-168, I-169, I-70, I-171, I-172, I-73, I-174, and I-175. At 23 knots, this type had the fastest surface speed for any submarine at the time of construction, although the speed was bettered slightly by later Japanese submarines. I-174 and I-175 were of the KD6B sub-type. They were 30 cm longer, 25 tons heavier, and were equipped with a 50 cal deck weapon instead of a 65 cal. ^[6]

KD6s contributed to the sinking of two American aircraft carriers during World War II. The destruction of these submarines also hold some milestones; I-70 was Japan's first major warship casualty in World War II, and the sinking of I-73 represented the first warship kill by a United States Navy submarine in the war. ^[6]

KD7

The final design in the Kaidai class, ten KD7s were ordered in 1939 (I-176, I-177, I-178, I-179, I-180, I-181, I-182, I-183, I-184, and I-185), and were completed over the course of 1942 and 1943. ^[7] Instead of possessing some aft-firing torpedo tubes as all other predecessors did, the KD7's 6 tubes all faced forward. They had an underwater endurance of 75 days. ^[8]

Seven of the ten KD7s were sunk within their first year of operation, and all ten vessels were sunk by October 1944. ^[8]

References

• Smith, A.E. [1991] (May 1992). Three Minutes of Time - the torpedoing of the Australian Hospital Ship Centaur, Second Printing, Miami: Tasman Press. ISBN 0-646-07631-0.