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] Two large, long-range Japanese submarines had already been built under the Eight-six fleet program as prototype (I-51 and I-52), 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.