They hoped for a speed of 36 knots (41 mph; 67 km/h), but otherwise, the requirements were similar to those that gave rise to the previous year's L-class.

[11][12] On 31 January 1915, Manly was one of seven destroyers of the Harwich Force dispatched to Sheerness to make part in minelaying operations east of the Straits of Dover to restrict the movements of German U-Boats.

[13] On 28 March, four destroyers of the Harwich force (Laurel, Liberty, Leonidas and Lucifer carried out an anti-submarine sweep off the Dutch coast.

[15] On 2 July 1915, Manly, together with Mentor and Miranda escorted the former ocean liner Empress of Britain, on passage from Liverpool to the Dardanelles.

Manly remained with Empress of Britain until 9:00 pm on 2 July, then set course to Queenstown to refuel, after which she was to rendezvous with the other two destroyers to escort the Aquitania, another Dardanelles-bound former ocean liner.

Manly ran aground in thick fog just outside Queenstown, however, leaving Aquitania with only Mentor and Miranda as escort.

[16] On 16 August 1915, 8 destroyers of the 10th Flotilla, including Manly, escorted the minelayer Princess Margaret which was tasked with laying a minefield on the Arum Bank.

[17][18] On 23 August 1915, 12 destroyers of the Harwich Force, including Manly, were attached to the Dover patrol to cover a bombardment of the German-held Belgian port of Zeebrugge by the monitors Lord Clive, Sir John Moore and Prince Rupert.

[21][22] On 25 December 1915, Manly was one of eight destroyers from the Harwich Force that were ordered with the leader Nimrod to the Channel as a result of attacks by the German submarine U-24.

[29][30] Manly transferred to the Dover Patrol on 8 May 1917,[31] and on 5 June escorted the monitors Erebus and Terror when they bombarded Ostend.