She became famous for the boarding of the German supply ship Altmark in Norwegian waters, and the associated rescue of sailors originally captured by the Admiral Graf Spee.

[5] The ships carried enough fuel oil to give them a range of 5,700 nautical miles (10,600 km; 6,600 mi) at 15 knots (28 km/h; 17 mph).

[6] The primary armament of the Tribal-class destroyers was eight quick-firing (QF) 4.7-inch (120 mm) Mark XII guns in four superfiring twin-gun mounts, one pair each fore and aft of the superstructure, designated 'A', 'B', 'X', and 'Y' from front to rear.

[11] To increase the firing arcs of the AA guns, the rear funnel was shortened and the mainmast was reduced to a short pole mast.

[12] Authorized as one of nine Tribal-class destroyers under the 1936 Naval Estimates,[13] Cossack was the sixth ship of her name to serve in the Royal Navy.

[15] On 7 November 1939 Cossack collided with SS Borthwick in the Firth of Forth en route from Scapa Flow to Leith Docks.

The Norwegian officers present later reported that only the mass of ice piled up prevented the destroyer being crushed onto the rocky shore.

With temporary repairs, Cossack refloated during the night at high tide and crawled her way stern-first to Skelfjord, Lofotens, where she was patched up sufficiently to limp home.

Later that year, she was part of the force which was assigned to hunt for a German surface raider that had been reported breaking out into the North Atlantic.

The report turned out to be false, so after spending a week at sea, including Christmas Day, she returned to port on New Year's Eve.

On 23 October 1941 Cossack was escorting a convoy from Gibraltar to the United Kingdom when she was struck by a single torpedo fired by the German submarine U-563 commanded by Klaus Bargsten.