5. The Soviets planned an invasion of Hokkaido in August 1945
At the Yalta Conference, Franklin Roosevelt secured a promise from Stalin to invade Japan, which was reiterated to Truman during the Potsdam Conference. Allied invasion planners in the Pacific were unaware that the Soviets were planning to keep that promise with an invasion of Hokkaido. In the spring of 1945, the United States initiated Project Hula, in which 180 ships were to be transferred to the Soviet Union via the Aleutians. The ships included landing craft, transport vessels, escort vessels, mine sweepers, and other support vessels. Since the Soviets had minimal experience with invasion from the sea, American and British advisors accompanied the ships.
American planners were aware of Soviet intentions in the Kuril Islands and the Sakhalin peninsula, by the planned invasion of Hokkaido, one of the major Japanese home islands, was unknown to the Americans. The Soviets went forward with their invasion of the Kuril Islands, attacking on August 18, 1945 – three days after the Japanese surrender. Fighting continued until September 1, with the Japanese troops in the islands offering a clue as to what could have been expected during an invasion of Kyushu. On August 23, under orders of the Japanese command, the majority of the troops surrendered, but isolated units continued to resist. The Soviets suffered about 2,000 casualties (out of 15,000 engaged) in what amounted to a Stalin land grab.