After the Japanese took control of much of the middle and lower Yangtze in the 1930s, American river gunboats entered into a period of inactivity and impotence. During the early-1930s, National Revolutionary Army took control of much of the north bank of the middle river. The climax of hostilities occurred in 1937 with the Rape of Nanking and the sinking of "Panay" by the Japanese. The USS "Panay" incident was the first loss of a U.S. Navy vessel in the conflict which would soon become World War II.