Japanese submarine Ro-2

Ro-2, originally named Submarine No. 21, was an Imperial Japanese Navy Type F submarine of the F1 subclass. She and her sister ship JAPANESE SUBMARINE Ro-1 were the first truly seagoing Japanese submarines, and the earliest to be classified as "second-class" or "medium" submarines of the Ro series. She was commissioned in 1920 and operated in the waters of Japan. She was stricken in 1932.

Design and description
The Type F submarines were designed by the Italian firm Fiat-Laurenti and built under license by Kawasaki at Kobe, Japan. They were the Imperial Japanese Navy′s first true seagoing submarines, and when the Japanese adopted a three-tiered classification system of its submarines as first-class (I), second-class or medium (Ro), and third-class (Ha) on 1 November 1924, the Type F submarines were the earliest to receive the second-class classification, as reflected in their low numbers in the Ro series, and in fact they were the earliest Japanese submarine classified as anything higher than third-class. They had non-cylindrical hulls intended to provide extra internal space, but the Japanese considered the hulls weak despite the provision of additional scantlings during construction to reinforce them. Because of their disappointing performance, they did not serve as the basis for any later Japanese submarine classes.

The submarines of the F1 subclass displaced 689 LT surfaced and 1,047 LT submerged. The submarines were 65.6 m long and had a beam of 6.1 m and a draft of 4.2 m. They had a diving depth of 40 m. For surface running, the submarines were powered by two 1,400 bhp Fiat diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a Savigliano 600 hp electric motor. They could reach 13 kn on the surface and 8 kn underwater. On the surface, they had a range of 3,500 nmi at 10 kn; submerged, they had a range of 80 nmi at 4 kn.

The submarines were armed with five 450 mm torpedo tubes, three in the bow and two in the stern, and carried a total of eight Type 44 torpedoes. As built, they were armed with a 7.7 mm machine gun. Soon after completion, however, a 76.2 mm deck gun was added.

Construction and commissioning
Ordered under the Japanese 1915–1916 naval program, Ro-2 was laid down as Submarine No. 21 on 1 July 1918 by Kawasaki at Kobe, Japan. Launched on 22 November 1919, she was completed and commissioned on 20 April 1920.

Service history
Upon commissioning, Submarine No. 21 was attached to the Kure Naval District. On 16 October 1920, she was assigned to Submarine Division 14 in Submarine Squadron 1 in the 1st Fleet. On 1 December 1920, she was reassigned to Submarine Division 21 in the Sasebo Defense Division in the Sasebo Naval District, and she spent the remainder of her career serving in this capacity. She was renamed Ro-2 on 1 November 1924.

Ro-1 was stricken from the Navy list on 1 April 1932.