Submarines of the Imperial Japanese Navy
The ("I-15"-class) submarines (, , , , , , , , , , , , , , , , , , , ) were the most numerous type of submarines of the Imperial Japanese Navy during World War II. In total 20 were made, starting with "I-15", the class ship. These were fast, very long ranged, and carried a single Yokosuka E14Y seaplane, located in a hangar in front of the conning tower, launched by a catapult.
Japanese submarine I-55 (1925)
Following World War I, the Imperial Japanese Navy re-evaluated the use submarine warfare as an element of fleet strategy due to the successful deployment of long-range cruiser-submarines for commerce raiding by the major combatant navies. 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. Two large, long-range Japanese submarines had already been built under the Eight-six fleet program as prototype ( and ), however, the arrival on 20 June 1919 of seven German U-boats received by Japan as war reparations at the end of World War I led to a complete re-design. The Japanese quickly hired hundreds of German submarine engineers, technicians and former U-boat officers unemployed by the defeat of Germany in World War I, and brought them to Japan under 5-year contracts. The American ONI (Office of Naval Intelligence) estimated that some 800 German advisors had gone to Japan by the end of 1920. The Japanese also sent delegations to Germany, and were active in purchasing many patents.