The were medium Imperial Japanese Navy submarines in commission during the 1920s. They were Japan's first true seagoing submarines and the earliest Japanese submarines classified as "second-class" or "medium" submarines.
The Type F submarines were designed by the Italian firm Fiat-Laurenti and built under license by Kawasaki at Kobe, Japan.[1] The Type F submarines were the Imperial Japanese Navy′s first true seagoing submarines,[1] 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,[2] the Type F submarines were the earliest to receive the second-class classification,[1] as reflected in their low numbers in the Ro series,[1] and in fact they were the earliest Japanese submarine classified as anything higher than third-class.
As built, Type F submarines had no deck gun, but soon after they were completed each of them had a 76.2mm/40 gun installed on her deck.[1] The Type F submarines 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.[1] Because of their disappointing performance, they did not serve as the basis for any later Japanese submarine classes.[1]
The Type F submarines were divided into two subclasses:
The F1 subclass was ordered under the 1915–1916 naval program.[1] Two were constructed between 1917 and 1920:[1] [3] [4]
| Name | Laid down | Launched | Completed | Notes, fate |
ex-Submarine No. 18 | 5 January 1917 | 28 July 1919 | 31 March 1920 | Renamed Ro-1 on 1 November 1924. Stricken 1 April 1932. |
ex-Submarine No. 21 | 1 July 1918 | 22 November 1919 | 20 April 1920 | Renamed Ro-2 on 1 November 1924. Stricken 1 April 1932. |
The F2 subclass (Ro-3-class) was ordered in 1918.[1] It was an improved version of the F1 subclass with a modified bridge.[1] The Fiat diesel engines were unreliable and the F2 subclass′s top surface speed of was well below the intended .[1] Additional F2 subclass units planned under the 1919 construction program were cancelled and replaced by the new Kaichū-type and Type L submarines.[1]
Three submarines of the F2 subclass were constructed between 1919 and 1922:[1] [5] [6] [7]
| Name | Laid down | Launched | Completed | Notes, fate |
ex-Submarine No. 31 | 28 October 1919 | 10 March 1921 | 15 July 1922 | Renamed Ro-3 1 November 1924. Stricken 1 April 1932. |
ex-Submarine No. 32 | 22 December 1919 | 22 June 1921 | 5 May 1922 | Renamed Ro-4 1 November 1924. Stricken and hulked 1 April 1932. |
ex-Submarine No. 33 | 1 March 1920 | 17 September 1921 | 9 March 1922 | Renamed Ro-5 1 November 1924. Stricken and hulked 1 April 1932. |
Sources[1]
| Type | F1 (Ro-1) | F2 (Ro-3) | |
| Displacement | Surfaced | 689LT | 689LT |
| Submerged | 1047LT | 1047LT | |
| Length (overall) | 65.6m (215.2feet) | 60.5m (198.5feet) | |
| Beam | 6.1m (20feet) | 6.1m (20feet) | |
| Draft | 4.2m (13.8feet) | 4.1m (13.5feet) | |
| Power plant and shaft | 2 × Fiat diesel engines 2 x Savigliano electric motors 2 shafts | 2 × Fiat diesel engines 2 x Savigliano electric motors 2 shafts | |
| Power | Surfaced | 2800bhp | 2600bhp |
| Submerged | 1200shp | 1200shp | |
| Speed | Surfaced | 13kn | 14kn |
| Submerged | 8kn | 8kn | |
| Range | Surfaced | 3500abbr=onNaNabbr=on at 10kn | 3500abbr=onNaNabbr=on at 10kn |
| Submerged | 75abbr=onNaNabbr=on at 4kn | 75abbr=onNaNabbr=on at 4kn | |
| Test depth | 40abbr=onNaNabbr=on | 40abbr=onNaNabbr=on | |
| Fuel | 58.4 tons | 58.4 tons | |
| Complement | 43 | 43 | |
| Armament | As built: • 5 × 4500NaN0 torpedo tubes (3 × bow, 2 × stern) • 8 × Type 44 torpedoes • 1 × 7.7 mm machine gun Added after completion: • 1 x 76.2mm deck gun | • 5 × 4500NaN0 torpedo tubes (3 × bow, 2 × stern) • 8 × Type 44 torpedoes • 1 × 7.7 mm machine gun Added after completion: • 1 x 76.2mm deck gun | |