"Engadine" was purchased in February 1915 by the Admiralty and she was modified by Cunard at Liverpool from 10 February to 23 March 1915 with a permanent, four-aircraft, hangar in the rear superstructure and a pair of cranes were mounted at the rear of the hangar to hoist the seaplanes in and out of the water. Four quick-firing (QF) 12-pounder 12 cwt guns, each with 130 rounds, and two Vickers QF 3-pounder anti-aircraft guns, each with 65 rounds, were fitted for self-defence. She also carried a pigeon loft that housed carrier pigeons to be used by her aircraft if their wireless was broken.