The submarines of the Kaichu V sub-class were designed for anti-shipping operations and carried more fuel and had greater range and a heavier gun armament than preceding Kaichu-type submarines. They displaced 8520NaN0 surfaced and 10200NaN0 submerged. The submarines were 74.22m (243.5feet) long and had a beam of 6.12m (20.08feet) and a draft of 3.73m (12.24feet). They had a diving depth of 45.7sp=usNaNsp=us.
For surface running, the submarines were powered by two 6000NaN0 Sulzer diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 600hp electric motor. They could reach 13kn on the surface and underwater. On the surface, they had a range of 9000nmi — although the Imperial Japanese Navy officially announced it as 6000nmi — at ; submerged, they had a range of 85nmi at .
The submarines were armed with four internal bow 533mm torpedo tubes and carried a total of eight torpedoes. They were also armed with a single 120mm deck gun and one 6.5 mm machine gun.
Ro-32 was laid down as Submarine No. 71 on 24 October 1921 by Kawasaki at Kobe, Japan.[1] Launched on 19 March 1923,[1] she was completed and commissioned on 31 May 1924.[1]
Upon commissioning, Submarine No. 71 was attached to the Sasebo Naval District, to which she remained attached throughout her active career.[1] On 15 June 1924, she was assigned to both Submarine Division 25 — in which she spent her active career — and the Mako Defense Division headquartered at Mako in the Pescadores Islands.[1] She was renamed Ro-32 on 1 November 1924.[1] On 1 December 1926, she was reassigned to the Sasebo Defense Division, headquartered at Sasebo, Japan.[1] Her service in the Sasebo Defense Division ended on 15 November 1934, after which she served as a unit of Submarine Division 25 in the Sasebo Naval District.[1]
Ro-32 was decommissioned and placed in the Fourth Reserve on 15 December 1938.[1] The Japanese struck her from the Navy list on 1 April 1942,[1] and that day she became a stationary training hulk at the submarine school at Ōtake, Japan.[1] She was scrapped ca. August 1945.[1]
During World War II, the United States Coast Guard cutter, the Coast Guard-manned United States Navy patrol vessel, and a Royal Canadian Air Force Bristol Bolingbroke maritime patrol aircraft of No. 115 Squadron shared credit for the sinking of a submarine in the Pacific Ocean off Southeast Alaska at 55.3333°N -174°W on 9 July 1942,[2] and in 1947 the Joint Army-Navy Assessment Committee identified the sunken submarine as Ro-32.[3] In 1967, the U.S. Navy retracted that finding after determining that Ro-32 had been inactive in Japan at the time of the sinking and had remained afloat through the end of World War II.[3] [4]