Moorsom also undertook other duties, including escorting the troop ship Mauretania in June 1915 and the minelayer Princess Margaret in August 1915 and November 1916.

Placed within the Dover Patrol, the destroyer formed part of the cover for monitors including Erebus and Terror on attacks on Ostend and Zeebrugge in May and June 1917, and April and May 1918.

[4] Three funnels were fitted and 296 long tons (301 t) of oil was carried, giving a design range of 3,450 nautical miles (6,390 km; 3,970 mi) at 15 knots (28 km/h; 17 mph).

[22] On 28 November, Moorsom once again escorted Princess Margaret on a mission, this time to lay 500 mines 20 nautical miles (37 km; 23 mi) west of Borkum.

[25] By 27 January, the destroyer was part of a flotilla, which also included Manly, Mansfield, Matchless, Morris, Nimrod and Phoebe, that was to patrol east of the Schouwen Bank.

[26] The force did not see the German ships, but Moorsom was nearly accidentally rammed by Starfish, which was part of another destroyer division operating in the area, due to the lack of visibility.

[30] The operation was deemed a success as the Admiralty gained intelligence that the bombardment led to the German command doubting that Ostend was a safe haven for their warships.

[32] The destroyer accompanied a subsequent attack on Zeebrugge by monitors on 23 April 1918, which also included the sinking of blockships to impede the flow of German submarines leaving the port.

[34] Although this operation did not meet the expectations of the Admiralty and the port remained open, the bombardment was achieved without interference by enemy warships or the loss of any British vessel.

[35] After the Armistice of 11 November 1918 that ended the war, the Royal Navy returned to a peacetime level of strength and both the number of ships and personnel needed to be reduced to save money.