The Japanese Invasion of French Indochina, also known as the Vietnam Expedition, was an attempt by the Empire of Japan, during the Second Sino-Japanese War to blockade China and prevent it from importing arms, fuel and 10,000 tons/month materials supplied by the United States through the Haiphong-Yunnan Fou railway line. Control of Vichy-controlled French Indochina would make the blockade of China more effective and made continuation of the drawn out Battle of South Guangxi province unnecessary.