(continued from KTB #109)

Three boats laid down as KAICHU TYPE 3 under 1917 program underwent so many modifications that they emerged as a new type; KAICHU TYPE 4. They were completed in 1924 - 1925 as BOAT #45, #48 and #62 (later Ro-26, Ro-27 and Ro-28 respectively). The most conspicuous change was their torpedo tubes. They now carried 53cm (actually 53.3cm = 21 inch) torpedoes. The externally mounted tubes were removed. The low-pressure blower was introduced to the main ballast tank. All those modifications led to the increase of the displacement, lowering the surface speed to 16 knots.

KAICHU TYPE 4 (Ro-26 CLASS)

Displacement............................................................805/1,080 tons
Length..........................................................74.22 meters (243' 6")
Beam...............................................................6.12 meters (20' 1")
Draught............................................................3.73 meters (12' 3")
Machinery..................................................twin-shaft diesel electric (diesels by Sulzer brothers)
Power (diesel).....................................................................2,600hp
Power (electric)...................................................................1,200hp
Speed (diesel).....................................................................16 knots
Speed (electric).................................................................8.5 knots
Fuel.....................................................................................75 tons
Radius of action (diesel)..............................6,000 miles @ 10 knots
Radius of action (electric).................................85 miles @ 4 knots
Tubes (fwd).........................................................four 21 inch tubes
Tubes (aft)..............................................................................none (carried 8 torpedoes aboard)
Guns........................single 8cm AA and single 6.5mm (.25 cal) MG
Depth of dive................................................45.7 meters (139 feet)
Crew...........................................................................................46

The introduction of the torpedo to the I.J.N. dates back to as early as 1884. In this year I.J.N. imported from Germany, the Schwalzkopf torpedo. Its performance was 400 meters (437 yards) at 22 knots.

In 1893 the I.J.N. further imported from Great Britain the Whitehead torpedo with better performance. It ran 800 meters (875 yards) at 24 knots, or 2,500 meters (1,735 yards) at 15 knots. Those were 35.6cm (14 inch torpedoes. They were 'cold-running' (propelled with unheated compressed air) type. The war with China (1894-1895) was fought with these imported torpedoes.

After the Sino-Japanese War, in 1897, the I.J.N. bought the license for the production of the 14 inch and 18 inch torpedoes from Whitehead, and started to produce them at Kure Navy Yard. The 18 inch torpedo was the 'dry-heat' (propelled by heated compressed air) type (an American invention) and ran 1,000 meters (1,094 yards) at 40 knots; 2,000 meters (2,188 yards) at 32 knots; or 4,000 meters (4,376 yards) at 23 knots.

Those locally made torpedoes were successfully used in the Russo-Japanese War (1904-1905). After the War, the I.J.N. improved the propulsion of the torpedo and finally, in 1911, succeeded in producing the genuine steam-propelled 18 inch and 21 inch torpedoes which were accepted to the service use as TYPE 44 torpedoes. The performance of the 21 inch version was 7,000 meters (7,658 yards) at 35 knots; or 10,000 meters (10,940 yards) at 27 knots. This was where the Japanese torpedo made its start.

The Holland boats carried Whitehead 'cold-running' 18 inch torpedoes (Japanese designation TYPE 38 MOD 1). They ran 1,000 meters (1,094 yards) at 27 knots; 2,000 meters (2,188 yards) at 24 knots; or 3,000 meters (3,282 yards) at 20 knots.

The C TYPE boats that followed carried the torpedo TYPE 38 MOD 3 that was 'cold-running' or the B MOD that was 'dry-heat'. The former ran 1,000 meters at 31.5 knots; 2,000 meters at 26 knots; or 3,000 meters at 20.3 knots. The latter ran 1,000 meters at 40 knots; 2,000 meters at 32 knots; or 4,000 meters at 23 knots. It is apparent from the above figures that the heating of the compressed air was quite a breakthrough in the torpedo propulsion technology.

The Japanese yards produced all the components of torpedoes except the air flasks. It required a very high level of machine tooling technology to produce those flasks which contained air under extremely high pressure. It took quite a while for the Japanese to attain this level of technology, and in the meantime, all the air flasks were imported.

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)