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. 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. 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.
Japanese submarine I-8
The Japanese submarine "I-8" was a World War II Junsen Type J-3 Imperial Japanese Navy submarine. The vessel, along with "I-7", were the largest Japanese submarines to be completed before the outbreak of the Pacific War. It was based on the KD ("Kaidai") type. Both submarines participated in the attack on Pearl Harbor, they also conducted patrol missions with Yokosuka E14Y seaplanes.
In 1943 "I-8" completed a technology exchange mission by sailing to German occupied France and back to Japan. Under a new commander later in her career, the submarine's crew committed several war crimes in the latter period of the second world war.