The ship was used as a despatch vessel on the China Station in the 1930s, but the Second World War resulted in her being rearmed, and used for escort duties.

[7] During the war, the 3-pounders and multiple machine gun mounts were removed, and first two, and later four single Oerlikon 20 mm autocannon added.

[9] After commissioning and workup, Falmouth was sent to the China Station where she was used as a despatch vessel for the commanding Admiral, allowing him and his staff to visit ports too small for the cruisers used as his flagship.

[11] In March 1934, Falmouth accompanied the cruiser Suffolk which carried Admiral Frederic Dreyer, the commander of the China Station, on a visit to the Philippines.

[16] In August 1937, in one of the opening actions of the Second Sino-Japanese War, hostilities broke out between Chinese and Japanese forces in Shanghai.

On 17 August 1937, Falmouth and the destroyer Duncan evacuated over 2000 British women and children from Shanghai down-river to Wusong, where the refugees were embarked on liners for onwards transfer to Hong Kong.

[18] On 4 October, Falmouth evacuated the British Ambassador to China, Hughe Knatchbull-Hugessen, who had been badly wounded when his car had been strafed by a Japanese aircraft, to Hong Kong.

[19][20] 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.

[21] In March 1940, Falmouth was refitted at Hong Kong to add Sonar and improve the ship's armament,[10] 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.

[27] On 25 August 1941 Britain and the Soviet Union invaded Iran, with Falmouth in charge of the landings at Khorramshahr, carrying two companies of the 3/10th Baluch Regiment.

[10] On 2 May 1943, the German submarine U-852 was attacked and badly damaged by a Vickers Wellington bomber from 621 Squadron RAF near Ras Hafun, Somalia.

[10] She was allocated to take part on Operation Zipper, the planned British seaborne invasion of Malaya in September 1945, but after the Surrender of Japan was diverted to Singapore.