In March 1940 HMS Falmouth was a unit of the Far Eastern Fleet, and based at Singapore. She was responsible for carrying out patrols in the Tjilatjap area. On 24 June, while in the Persian Gulf, she succeeded in sinking the Italian submarine Galvani.

In April 1941 Falmouth was involved in the escorting of troop convoys from Karachi to Basra. On August 25th, Falmouth in company with the sloops, HMS Shoreham and the Australian HMAS Yarra, were involved in operation "Countenance", this was the entry into Iran by British forces from the south. Commodore Cosmo Graham was placed in command of the naval operations, and in response to his request for additional forces the CinC East Indies, Vice Admiral Arbuthnot offered him the Australian armed merchant cruiser HMAS Kanimbla. Surprise was essential for the speedy success of the undertaking. Falmouth was responsible for transporting two platoons and company headquarters of the 3/10th Baluch Regiment which dealt with the Iranian naval base of Khorramshahr. The operation was a complete success.

From January 19-February 2nd 1944 Falmouth was docked in the Selborne dry dock at Simonstown, South Africa. On February 2nd, she was undocked.

In January 1952, Falmouth became the RNVR ship Calliope. In April 1968, Calliope was broken up for scrap by Hughes Bolckow of Blyth.

Her badge can be seen displayed on the side of the Selborne dry dock wall with the inscription "Fail Not".