During the Spanish Civil War of 1936–1939, the ship enforced the arms blockade imposed by Britain and France on both sides as part of the Mediterranean Fleet.

[1] Hyperion carried a maximum of 470 long tons (480 t) of fuel oil that gave her a range of 5,530 nautical miles (10,240 km; 6,360 mi) at 15 knots (28 km/h; 17 mph).

For anti-aircraft (AA) defence, Hyperion had two quadruple Mark I mounts for the 0.5 inch Vickers Mk III machine gun.

[5] The ship's anti-aircraft armament was increased when the rear set of torpedo tubes was replaced by a 12-pounder 12 cwt[Note 1] AA gun, although when exactly the modification was made is not known.

[8] When World War II began on 3 September, the ship was en route to Freetown, Sierra Leone, to search for German commerce raiders.

Hyperion was transferred to the North America and West Indies Station in late October where he blockaded various German merchant ships in American and Mexican harbours.

The ship and her sister Hero pretended to lay a minefield off Bud, Norway on 8 April and reported its location to the Norwegians.

[8] On 9 July she participated in the Battle of Calabria as an escort for the heavy ships of Force C and unsuccessfully engaged Italian destroyers and suffered no damage.

[8] Hyperion struck a mine on 22 December 1940 off Pantelleria as she escorted the battleship HMS Malaya on passage from Alexandria to Gibraltar while covering a convoy to Malta.