In 1937, the complexion of life for the Yangtze gunboats changed. The undeclared Second Sino-Japanese War began in July and spread to the Yangtze valley in August–September. Japanese river operations effectively bottled up the river for neutral gunboats, and their proximity to war zones produced incidents such as the sinking of by Japanese aircraft on 12 December 1937. On 3 August 1938, "Tutuila" followed up the river to Chungking, as the YangPat flagship carried the American Ambassador—Nelson T. Johnson—to that river port.