On 1 January 1915, the battleship was torpedoed and sunk by the German submarine in the English Channel. "Matchless", at sea at the time, was diverted to take part in the search for "U-24". "Matchless" joined the Harwich Force, which operated in the North Sea and could reinforce the Grand Fleet or forces in the English Channel as required. On 31 January 1915, "Matchless" 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. They continued escorting the minelayer until 9 February. By June 1915, "Matchless" was listed as part of the 10th Destroyer Flotilla, as part of the Harwich Force. On 13 June 1915, the 10th Destroyer Flotilla, including "Matchless", was ordered to Avonmouth for operations in the South-West Approaches, and in particular, to escort troopships carrying the 13th Division to the Middle East on the initial part of their journey, with two destroyers per transport. After the 13th Division had all left, the 10th Flotilla continued on escort duties based at Devonport, escorting the ships carrying the next division to be sent to the Gallipoli campaign, the 12th Division. The 10th Flotilla was relieved from its escort duty in July 1915, allowing it to return to Harwich. On 16 August 1915, 8 destroyers of the 10th Flotilla, including "Matchless", escorted the minelayer which was tasked with laying a minefield on the Arum Bank. The force encountered five patrolling German destroyers, and the German destroyer torpedoed the destroyer , blowing off "Mentor"s bows, and then turned away. This caused the operation to be abandoned. Despite the damage, "Mentor" made it safely back to Harwich. On 30 October "Matchless" took part in a sweep by the Harwich Force of the German Bight during which the Swedish steamer "Osterland" was stopped and sent to the Humber for investigation of a suspicious cargo of iron ore.