The submarines of the K6 sub-class were versions of the preceding K5 sub-class with greater range and diving depth. They displaced 11150NaN0 surfaced and 14470NaN0 submerged. The submarines were 80.5m (264.1feet) long, had a beam of 7m (23feet) and a draft of 4.07m (13.35feet). They had a diving depth of 80m (260feet).[1]
For surface running, the boats were powered by two 21000NaN0 diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 600hp electric motor.[2] They could reach 19.75kn on the surface and underwater. On the surface, the K6s had a range of 11000nmi at ; submerged, they had a range of 45nmi at .
The boats were armed with four internal bow 53.3cm (21inches) torpedo tubes and carried a total of ten torpedoes. They were also armed with a single 76.2mm L/40 anti-aircraft gun and two single 251NaN1 AA guns.[3]
Ro-38 was laid down as Submarine No. 204 on 20 June 1942 by Mitsubishi at Kobe, Japan.[4] She was renamed Ro-38 on 1 November 1942,[4] and was provisionally attached to the Maizuru Naval District that day.[4] She was launched on 24 December 1942[4] and completed and commissioned on 24 July 1943.[4]
Upon commissioning, Ro-38 was attached formally to the Maizuru Naval District,[4] and on 31 July 1943 she was assigned to Submarine Squadron 11 for workups.[4] On 31 October 1943 she was reassigned to Submarine Division 34 in the 6th Fleet, and she departed Maizuru bound for Truk that day. She arrived at Truk on 8 November 1943.[4]
Ro-38 got underway from Truk on 19 November 1943 to begin her first war patrol, assigned a patrol area in the Gilbert Islands in the vicinity of Makin and Tarawa.[4] The Japanese never heard from her again.[4]
On 20 November 1943, the Battles of Makin and of Tarawa began with the U.S. landings on those atolls. That day, the commander-in-chief of the 6th Fleet, Vice Admiral Takeo Takagi, ordered Ro-38 and the submarines,,,,,,, and to attack the U.S. invasion fleet off the atolls.[4] On 26 November 1943, Takagi ordered I-19, I-40, I-169, and Ro-38 to form a patrol line north of Makin, with Ro-38 northeast of Makin at the eastern end of the line.[4] The 6th Fleet ordered Ro-38 to move to a new patrol area southeast of Tarawa on 27 November 1943,[4] and on 4 December 1943 it sent her orders to patrol between Tarawa and Canton Island.[4] Ro-38 did not acknowledge any of these orders.[4]
The circumstances of Ro-38′s loss are unknown. It is possible that the United States Navy destroyer sank her west of Tarawa on 24 November 1943.[4] On 2 January 1944, the Imperial Japanese Navy declared her to be presumed lost off the Gilbert Islands with all 77 hands.[4] She was stricken from the Navy list on 30 April 1944.[4]