The Admiralty M class were improved and faster versions of the preceding .[1] They displaced 971LT. The ships had an overall length of 273feet, a beam of 26feet and a draught of 9feet. They were powered by three Parsons direct-drive steam turbines, each driving one propeller shaft, using steam provided by four Yarrow boilers. The turbines developed a total of 25000shp and gave a maximum speed of 34kn. The ships carried a maximum of 237LT of fuel oil that gave them a range of 2100nmi at . The ships' complement was 76 officers and ratings.[2]
The ships were armed with three single QF 4adj=onNaNadj=on Mark IV guns and two QF 1.5-pounder (37 mm) anti-aircraft guns. These latter guns were later replaced by a pair of QF 2-pounder (40 mm) "pom-pom" anti-aircraft guns. The ships were also fitted with two above water twin mounts for 21inches torpedoes.[2]
Onslow was ordered under the Third War Programme in November 1914 and built by Fairfield Shipbuilding & Engineering Company at Govan. The ship was launched on 15 February 1916 and completed in April 1916.[3] Her first commander was John Tovey, (later Admiral of the Fleet).
On 24 April 1916, the Easter Rising against British rule broke out in Ireland. Two infantry brigades were ordered from Liverpool to Dublin to reinforce the British forces, with Onslow escorting the transports carrying these troops.[4] She saw action at the Battle of Jutland and was badly damaged, with her speed reduced to . Tovey pressed home the attack against first a cruiser and then a line of battlecruisers. Onslow was brought back to Aberdeen despite the damage, having been towed out of action by the destroyer, under heavy fire. The report on the battle by Admiral Beatty stated that:
Both officers were awarded DSOs.
Onslow was sold for breaking up on 26 October 1921.