'Longtom' was the Allied overall designation of unrealised plans for landings on the coast of mainland China in the area of Shanghai, the seizure of the approaches to the Japanese home islands, and the intensification of aerial bombing and mining attacks to support a prolonged blockade of the home islands (spring 1945).

The primary element of the plan was an amphibious descent on the Chusan islands group, off the coast of China just to the south-east of Shanghai, and the nearby Ningpo peninsula, on the southern side of the Yangtze river estuary, and was proposed by Admiral Raymond A. Spruance but taken in hand only for contingency planning (spring 1945).

The undertaking had been tentatively scheduled for launch in August 1945, but was cancelled in May 1945 after the decision had been taken to invade and defeat Japan militarily rather than starve the nation into submission.