Kaichu Type 5 (Ro-33 Class)

Ro-33 was launched in 1934 and completed in 1935-1
Ro-34 was launched in 1935 and completed in 1937,
Displacement 700/1,200 tons
Length 73 meters (248' 4")
Beam 6.7 meters (21' 11")
Draft 3.2 5 meters (12' 11")
Machinery twin shaft diesel/electric
Power (diesel) 2,900 bhp
Kampon diesels (electric) 1,200 ehp
Speed (diesel) 19 knots
Speed (electric) 8.2 knots
Bunkers 108.7 tons
Radius (diesel) 8,000 miles @ 12 knots (diesel) 90 miles @ 3.5 knots
Tubes (fwd) four 21 inch and (aft) none (carried 10 torpedoes)
Guns 80mm (3.1 inch) AA/40 cal
AA Guns single 13mm (.51 inch) machine gun
Depth of dive 75 meters (246 feet)
Crew 61 men

I.J.N. had not built medium-sized Ro-boats since 1923, but the tonnage restriction under the London Naval Treaty forced it to build small sized summaries again. This class was experimental prototypes for emergency wartime mass-production. They used the new diesel engine developed by Mitsubishi Shipyard Company, which was very fuel- efficient. They were very fast, and with a great operational radius. In general, they were very successful, with good sea-keeping quality and a great diving depth.

Kaidai Type 6a (I-68 [168] Class)

I-68 was launched in 1933 & completed in 1934, renumbered I-168 in 1942
I-69 was launched in 1934 & completed in 1935, renumbered I-169 in 1942;
I-70 was launched in 1934 and completed in 1935;
I-71 was launched in 1934 & completed in 1935, renumbered I-171 in 1942;
I-72 was launched in 1935 & completed in 1937, renumbered I-172 in 1942
I-73 was launched in 1935 & completed in 1937, renumbered I-173 in 1942.

Displacement 1,400/2,440 tons
Length 104.7 meters (336' 7")
Beam 8.2 meters (26' 11 ")
Draft 4.5 8 meters ( 15')
Machinery twin shaft diesel/electric
Power (diesel)
9,000 bhp two stroke Kampon diesels
Power (electric) 1,800 ehp
Speed (diesel) 23 knots
(electric) 8.2 knots
Bunkers 338 tons
Radius (diesel) 14,000 miles @ 10 knots
(electric) 65 miles@ 3 knots
Guns single 10cm (3.9 inch) AA/50 cal
AA Guns single 13mm (.51 inch) machine gun single 7.7 mm (.303 inch) machine gun
Depth of dive 70 meters (230 feet)
Crew 68 men

The most outstanding feature of this class was the new Kampon double-acting (two pistons per cylinder) two-cycle diesel engine. M.A.N. had made double-acting diesels, which were being used in merchant ships. I.J.N. entered into negotiations with M.A.N. to purchase the building license of this engine, but the price offered was too high. Therefore, I.J.N. began to develop a similar engine through its own effort, and was successful after several years hard work.

This engine was truly a miracle. It was much lighter than the Sulzer or M.A.N. built by predecessor, but 50% more powerful. With this engine, this class logged 24.02 knots with the emergency output of 9,561 horsepower. This was the greatest speed ever registered by a submarine in history. (The Royal Navy's K-Class submarine had once made 24 knots, but it was steam-driven and was purely experimental). As a KAIDAI type, this class was small (1,400 tons) to make the best use of tonnage allowed by the London Treaty.

This class was equipped with a new torpedo director (Type 91 mod 1) and it had two periscopes. Traditionally I-boats had three periscopes one for daylight use, the second for night use and the third for navigation but from this class on, the night periscope was used for navigation as well. The I-168 class is notable in that it made U.N. independent of all foreign technologies.

I-168 sank the carrier UKV YORKTOWN in the Battle of Midway.

This great history from YOYA will continue next month in KTB #138. Remember - if any other researchers would like to tackle a similar project for the Royal Navy (or any other) submarines, we would be happy to accept your articles. Thanks in advance.