On the outbreak of the Second World War in September 1939, "Falmouth" remained on the China Station, carrying out patrols near Hong Kong to intercept any German shipping. In March 1940, "Falmouth" was refitted at Hong Kong to add Sonar and improve the ship's armament, and then from 23 March became part of the British Malaya Force - a force of British warships keeping watch on German merchant ships in Dutch East Indies harbours. "Falmouth" was to watch Tjilatjap in Java, where the German merchant ship "Strassfurt" was present. The German merchant ships were seized by the Dutch following the German invasion of the Netherlands in May 1940. "Falmouth" was then sent to Colombo in Ceylon (now Sri Lanka), before being deployed to the Persian Gulf. On 21 June 1940, "Falmouth" sank the off the entrance to the Gulf. "Falmouth" remained operating in the Gulf until December 1940, when she was refitted at Bombay.