[2] Wartime modifications included the addition of a 2-pounder (40 mm) pom-pom anti-aircraft autocannon, the provision of depth charges, which may have resulted in one of the ship's guns and a pair of torpedo tubes being removed in 1918 to accommodate an outfit of 30–50 depth charges, while the ship was also modified to allow a kite balloon to be operated.
On 5 August 1914, the Third Destroyer Flotilla, led by the light cruiser Amphion and including Lark, carried out a sweep to prevent German minelayers or torpedo craft entering the English Channel.
[9][10][11][12] On 28 August 1914, the Harwich Force, supported by light cruisers and battlecruisers of the Grand Fleet, carried out a raid towards Heligoland with the intention of destroying patrolling German torpedo boats.
[15] On 24 October 1914, Lark set out from Harwich as part of the escort for the seaplane carriers Engadine and Empress on a raid against the German airship base at Cuxhaven.
The force reached the launch-off point off Heligoland on the morning of 25 October, but poor weather meant that only two of the six seaplanes managed to take-off, both of which quickly abandoned the mission.
[16] On 2 November 1914, the light cruiser Aurora, together with Lark and the destroyers Lawford and Laverock, left Harwich to patrol on the Broad Fourteens in search of German submarines.
[18][19] On 15 December 1914, the Germans staged a raid with their battlecruisers against the British East Coast towns of Scarborough, Whitby and Hartlepool.
[20][21] On 23 January 1915, the German battlecruisers under Admiral Franz von Hipper made a sortie to attack British fishing boats on the Dogger Bank.
[25] On 1 May 1915, the German submarine SM UB-6 torpedoed and sank the old British destroyer Recruit near the Galloper Light Vessel, off the Thames Estuary.
Four destroyers of the Harwich Force, Lark, Laforey, Lawford and Leonidas set out to hunt for Recruit's assailant.
[29] On 20 February 1916, part of the Ninth Flotilla, including Lark set out from Harwich to cover minesweeping operations.
[34] On 5 September 1916, Lark and Laurel were deployed to the English Channel to escort Princess Victoria, carrying a load of Gold bullion from Cherbourg to Portsmouth.
[35] The destroyers of the Harwich Force were regularly detached to the Channel to strengthen the defences of the Dover Patrol against potential attack by German surface forces, and in late October 1916, Lark was part of a division of four destroyers led by Lawford[b] that was taking its turn reinforcing the Dover Patrol.
Lark and the destroyer Myngs were ordered to reinforce the ships patrolling the barrage after the attack, but the Germans had already left.
The merchant ships arrived safely, but at around 16:30, after the destroyers had begun the return trip, Laforey struck a mine, breaking in half and sinking.
[55] By June 1919, Lark was listed as being laid up in reserve at The Nore,[56] and on 28 November 1919, her crew was reduced to a Care and Maintenance Party.