Japanese submarine I-51

Following World War I, the Imperial Japanese Navy General Staff began to re-consider submarine warfare as an element of fleet strategy. Before the war, the Japanese Navy regarded submarines as useful only for short-range coastal point defense.[1] However, based on the success of the Imperial German Navy in deployment of long-range cruiser-submarines for commerce raiding Japanese strategists came to realize possibilities for using the weapon for long range reconnaissance, and in a war of attrition against an enemy fleet approaching Japan.[1] Procurement for a large, long-range Japanese submarine was authorized in fiscal 1918 under the Eight-six fleet program, under the designation S22.

Project S22 was based on the latest Royal Navy design, the British K class submarine. Japanese ties to Great Britain via the Anglo-Japanese Alliance were still strong. Project S22 was laid down at Kure Naval Arsenal on 6 April 1921, launched on 29 November 1921 and completed on 20 June 1924.[2]

During construction, the vessel was renamed Submarine No.44 (第四四号潜水艦, Dai-Yonjūyon-go sensuikan), however, on commissioning into the Imperial Japanese Navy, her name was formally registered as I-51.

With a displacement of 1390 tons, I-51 was the largest submarine built in Japan to date. In order to attain a design speed of 23 knots on the surface, and 15 knots submerged, the design required four diesel engines, driving four screws. To accommodate these engines, a double hull design was used, with hulls joined side-by-side forming a sideways figure "8".

As completed, I-51 achieved only 18.4 knots surfaced and 8.4 knots submerged during trials, but had an unrefueled range of 20,000 nautical miles, which was considered remarkable for the time.[1]

I-51, despite her various technical achievements, as not regarded as a successful design, largely through problems with her Sulzer diesel engines. The vessel was never assigned to fleet service, but was retained at Kure Naval Arsenal for crew training and as a test bed for various submarine technologies.

In 1931, I-51 was fitted with an aircraft hangar housing a Yokosuka Ro-go Ko-gata floatplane, which could be raised and lowered into the water by a crane. In 1933, this was modified with the addition of an aircraft catapult, making I-51 the forerunner of the Japanese submarine aircraft carriers of World War II.

In 1932, two of her engines and associated shafts were removed, as was her main gun.[2]

I-51 was removed from the navy list on 1 April 1940 and was scrapped in 1941.

• Boyd, Carl (2002). The Japanese Submarine Force in World War II. Annapolis, MD: Naval Institute Press. ISBN 1557500150.
• Peattie, Mark R. (1997). Kaigun: Strategy, Tactics, and Technology in the Imperial Japanese Navy, 1887-1941. Annapolis, MD: Naval Institute Press. ISBN 0-87021-192-7.
• Jentsura, Hansgeorg (1976). Warships of the Imperial Japanese Navy, 1869-1945. Annapolis, MD: Naval Institute Press. ISBN 0-87021-893-X.
• Stille, Mark (2007). Imperial Japanese Navy Submarines 1941-45. Osprey. ISBN 1846030900.

• Nishida, Hiroshi. "Materials of IJN". Imperial Japanese Navy.