[6] The ship was powered by two geared steam turbines driving two shafts, fed by two Admiralty 3-drum boilers.

This machinery produced 2,000 shaft horsepower (1,500 kW) and could propel the ship to a speed of 16.5 knots (30.6 km/h; 19.0 mph).

[6] While previous ships of the class had been built with a gun armament of 4.7-inch (120 mm) low-angle guns, designed for use against surface targets, by 1934 it was realised that attack from the air posed a significant risk to shipping, and it was decided to fit the sloops of the 1934 programme with an improved anti-aircraft armament.

[5] The ship's depth charge loading increased to 60–90 during the war,[7][10] while a Hedgehog anti-submarine mortar was fitted in 1943.

[5] After commissioning, Fleetwood served as trials ship for the new armament, and then visited Gibraltar, Tangier and Cartagena, Spain during February–March 1937.

[11][12] Fleetwood was recalled to Home waters following the outbreak of the Second World War, arriving at Portland on 11 October 1939 and was tasked with providing escort to convoys along the East coast of Britain.

[16] On 27 May 1940, Fleetwood helped escort the badly damaged destroyer Eskimo, which had her bow blown off at the Second Battle of Narvik, from Harstad back to Britain.

Fleetwood returned to Britain in August 1941 when she was refitted at Middlesbrough, where radar was fitted and her anti-aircraft armament improved.

[19][12] In April 1943, Fleetwood returned to Londonderry, joining the 39th Escort group on the Freetown route.

[20][12] On 11 May 1943, Fleetwood was part of the escort of Sierra Leone-bound convoy OS47, when a Handley Page Halifax patrol aircraft of 58 Squadron RAF spotted the German submarine U-528, which was returning to France after being damaged by a previous air attack, and attacked with depth charges.

Fleetwood rescued 39 of U-528's crew, including her commanding officer, while Mignonette picked up 6 more and 11 men were killed.

[20][12] She was selected to serve as a Radar Training ship attached to the ASRE, and was refitted at Portsmouth, her armament being removed and her bridge enlarged to give increased accommodation.