The Yanagi missions took place under the Axis powers' Tripartite Pact to provide for an exchange of strategic materials and manufactured goods between Germany, Italy, and Japan. Initially, cargo ships made the exchanges, but when that was no longer possible, submarines were used. Only seven submarines attempted the trans-oceanic voyage: I-30 (April 1942), I-8 (June 1943), I-34 (October 1943), I-29 (November 1943), I-52 (March 1944) and the German submarines U-180 and U-511 (August 1943).