Instigated by the successful operations of German U-Boats in the Atlantic, I.J.N. made great efforts to strengthen its submarine fleet. Kawasaki Dockyard Company approached the Italian firm Fiat-Laurenti which was building submarines of extremely advanced design towards the beginning of the GREAT WAR. In 1915, Kawasaki purchased the license from Fiat to build the submarines and diesel engines of the Italian design. The Italian submarine was double-hulled and incorporated a great many novel features. For instance, its hydroplanes (bow and stern) were retractable. Its AA armament was also retractable. Its engines, both diesel and electric, were more powerful than any previous models.

At first, Kawasaki built two units of this type, but perhaps the Japanese ship-building technology was not quite up to this complicated boat. The two boats (Boat #18 and #21; later Ro-1 and Ro-2 respectively) were completed one after another in 1920 but in the trials, they developed many troubles. The engines were faulty. The hulls developed serious distortions at depths of only 20 meters (61 feet) or sometimes even less. This boat was great on paper, but in practice, it was a disappointment.

F-1 (Ro-1) TYPE

Displacement 689/1,047 tons
Length 65.58 meters
Beam 6.17 meters
Draft 4.19 meters
Power twin-shaft diesel-electric (diesels by Fiat; electric motors by Savigliano)
Speed (diesel) 17.8 knots, (electric) 8.2 knots
Fuel 58.4 tons
Radius of action (diesel) 3,500 miles @ 10 knots, (electric) 75 miles @ 4 knots
Tubes (fwd) three 18 inch tubes, (aft) two 18 inch tubes
Guns single 7.5cm AA gun
Depth of dive 50 meters (153 feet)
Crew 43

The Fiat boats disappointed I.J.N. but three more of them were already under construction when the faults of the design were revealed Kawasaki did their best to eliminate the bugs in the boats then under construction. The hulls were strengthened, but the license-built engines never worked well. The three units completed in 1922 (Boat #31; #32 and #33 later Ro-1; Ro-3 and Ro-4 respectively) could make only about 14 knots on the surface, due to the faulty engines. The production of Fiat boats was abandoned after building five units, and I.J.N. had to look around elsewhere to find a more reliable design.

F-2 (Ro-3) TYPE
Displacement 689/1,047 tons
Length 57.58 meters
Beam 6.07 meters
Draft 4.04 meters
Power twin-shaft diesel-electric (diesels by Fiat; electric motors by Savigliano)
Speed (diesel) 14.3 knots (electric) 8 knots
Fuel 58.4 tons
Radius of action (diesel) 3,500 miles @ 10 knots, (electric) 75 miles @ 4 knots
Tubes (fwd) three 18 inch tubes, (aft) two 18 inch tubes (carried 8 torpedoes on board)
Guns single MG
AA guns single 8cmAA retrofitted)
Depth of dive 30 meters (92 feet)
Crew 43

More History of the Japanese Submarine Navy

Part 1: 1905
Part 2: 1912-17
Part 3: C-1 and C-2
Part 4: Ha-9, Ha-10 and Tsing-Tao
Part 5: Ro-11, Ro-13, Ro-16
Part 6: Ro-1, Ro-3
Part 7: Kaichu Type 4
Part 8: Batteries
Part 9: Ro-57 and Ro-60
Part 10: I-16
Part 11: O-1 (ex U-125) and O-2 (ex U-46)