Another problem which the fledgling Japanese industry had to cope with was the production of the batteries. At first, all the batteries were imported. The first home-made batteries were used in Ro-12, the second unit of Ro-11 Class in 1919, but this batch of batteries had very low performance. After 30 to 50 discharges for two hours period, the capacity of the batteries went down by 50 per cent. The first two Fiat boats (Ro-1 and Ro-2) used Italian batteries (120 cells). But the later Fiat boats (Ro-3 through Ro-5) used Japanese batteries with twice the number, 240 cells. This was owing to the low standard of the Japanese metallurgical industry.

Periscopes were also problems. At first, British, German, and Italian periscopes were imported. The first locally-made periscope of 7 meters (23 feet) was used in Ro-16 in 1921. For the production of periscopes, Nihon Kogaku K.K.; a subsidiary of the Mitsubishi Heavy Industries; was established. This company was to grow into the giant, famous for the Nikon camera it produces. Type-88 Periscopes, which were the copy of the Ziess 9 meter (29.5 feet) periscope were widely used.

Under 1918 program, I.J.N. constructed four submarines of somewhat different characteristics from the preceding KAICHU Type. They had smaller and more economical engines with heavy loads of fuel, resulting in a very long radius of operation. They also had heavier artillery armament. They were called KAITOKUCHU, the acronym of KAIGUN TOKUBETU CHUGATA (Admiralty Special Medium Type) or sometimes simply TOKUCHU. It is assumed from their characteristics that they were built for the long-range reconnaissance purpose. Some consider them as forerunners of commerce-raiding submarines, but for that purpose, the number of torpedoes they carried was miserably small.

BOAT #	LATER DESIGNATION	COMPLETED
68	Ro-29	1923
69	Ro-30	1924
70	Ro-31	1927 *
71	Ro-32	1924

* Ro-31 was lost in trials on 21 August, 1923 while running trials off Kobe with 88 men lost in this mishap. The cause of the accident is said to be the mishandling of the low-pressure blower system. The boat was salvaged, repaired and commissioned at a later date.

KAITOKUCHU-TYPE (Ro-29 Class)

Displacement: 852/886 tons
Length: 74.22 meters (234' 6")
Draught: 3.73 meters (12' 3")
Machinery: twin shaft Sulzer diesels of 1,200 bhp, two electric motors of 1,200 ehp
Speed (diesel): 13 knots
Speed (electric): 8.5 knots
Fuel: 43 tons
Radius (diesel): 9,000 miles @ 10 knots
Radius (electric): 85 miles @ 4 knots
Tubes: four 21 inch fwd only (carried 8 torpedoes)
Guns: single 12cm/40 cal low angle deck gun
AA Guns: single 6.5cm/25 cal MG
Depth of dive: 45.7 meters (139 feet)
Crew: 44

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)