Type F submarine

Class overview
Name	Type F submarines
Builders	Kawaski, Kōbe, Japan
Operators	Imperial Japanese Navy
Preceded by	None
Succeeded by	Type L submarine
Subclasses	Type F1 (Ro-1-class) Type F2 (Ro-3-class)
Built	1917–1922
In commission	1920-1932
Completed	5
Retired	5

The Type F submarines (F型潜水艦, F-gata Sensuikan) 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 76.2 mm (3 in)/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:

• Type F1 (F1型（呂一型）, Ro-ichi-gata, Ro-1-class)
• Type F2 (F2型（呂三型）, Ro-san-gata, Ro-3-class)

The F1 subclass was ordered under the 1915–1916 naval program.^[1] Two were constructed between 1917 and 1920:^[1][3][4]

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 14 knots (26 km/h; 16 mph) was well below the intended 17 knots (31 km/h; 20 mph).^[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]

Sources^[1]

• Gray, Randal, ed., Conway′s All the World′s Fighting Ships 1906–1921, Annapolis, Maryland: Naval Institute Press, 1985, ISBN 0 87021 907 3.