Although not a successful design, she was the lead vessel and prototype of the Japanese Kaidai-class submarines which served in World War II.

Following World War I, the Imperial Japanese Navy General Staff began to re-consider submarine warfare as an element of fleet strategy.

However, based on the success of the Imperial German Navy in deploying long-range cruiser submarines for commerce raiding during World War I, Japanese strategists came to realize the potential for using submarines for long-range reconnaissance, as well as in a war of attrition against an enemy fleet approaching Japan.

[1] Procurement of a large, long-range Japanese submarine was authorized in fiscal year 1918 under the Eight-six fleet program, under the designation Project S22.

Japanese ties to the United Kingdom via the Anglo-Japanese Alliance were still strong in the immediate aftermath of World War I, and Project S22 was based on the latest Royal Navy design, the British K-class submarine.

[6] In 1931 she was fitted with an aircraft hangar which could house one floatplane which could be raised and lowered into the water by a crane, and she began testing the operation of the second E6Y prototype, the Yokosho 2-Go Kai.

[2] After the deactivation of Submarine Division 17 on 15 November 1935,[4] I-51 was attached directly to the Kure Naval District, and she continued her training duties until she was decommissioned and placed in the Fourth Reserve on 15 December 1938.