Displacement 1,390/2,430 tons
Length 91.44 meters (330’ 10”)
Beam 8.81 meters (25’ 1”)
Draft 4.6 meters (16’ 10”)
Machinery 4 shaft diesel/electric
Power (Sulzer Diesels) 5,200 bhp
Power (electric) 2,000 ehp
Speed (diesel) 18.4 knots
Speed (electric) 8.4 knots
Fuel 580 tons
Radius (diesel) 20,000 miles @ 10 knots
Radius (electric) 100 miles @ 4 knots
Tubes (fwd) six 21 inch tubes)
Tubes (aft) two 21 inch tubes) (carried 24 torpedoes)
Deck gun single 12cm (4 inch/45 cal)
AA Guns none
Depth of Dive 45.7 meters (150 feet)
Crew 70 men

KAI (gun) DAI (Large Admiralty) TYPE I was completed in 1924 as Boat #44. It was re-named I-51 in the same year. It was the first I-Boat planned and built. Since about 1917, I.J.N. had planned to build submarines with a range of 20,000 and a surface speed of over 20 knots. To fulfill these requirements a powerplant with an output of 6,000 was needed. I.J.N. therefore, asked the Sulzer Company of Switzerland to build this engine but it would take time. Time was running out. In order to solve the problem, it was decided to mount four diesel engines with an output of 1,300 hp each in the new boat. With each engine geared to a shaft, the boat had four shafts and four propellers.

This was the first submarine in the world with four shafts. To accommodate these four engines, the engine compartment consisted of two tubes each with a diameter of 4.5 meters placed side by side, each containing two engines. To obtain the tremendous range of 20,000 miles the boat carried 580 tons of diesel fuel. Dr. Ing. H. Techel, formerly of Krupp’s GERMANIA yard, offered assistance in the design work. In spite of the great effort put into the boat, the result was disappointing. the maximum surface speed was only 18.4 knots. The boat was used for training and experiments of new equipment. In 1931, experiments were conducted aboard this submarine to launch and recover an aircraft, using a YOKOSHO 2-GO reconnaissance seaplane. A water-tight stowage hangar was installed aft of the conning tower. In 1933 a catapult was installed on the aft deck, and a seaplane was successfully launched from the catapult. Although experimentally, I-51 was the first Japanese submarine that was equipped with a catapult.