The 21st Bombardment Squadron was one of the first squadrons to make a land-based attack on the Japanese home islands on 18 July 1943, flying B-24 Liberators. This raid, against Shimushu and Paramushiru in the Kuril Islands, caused little or no damage, but was only the first of a long series of attacks on Japan from the north. Inactivated in 1943; the 21st later was reorganized as a B-29 Superfortress Bomb Squadron and engaged in combat over Japan in 1945.