SS "Engadine" was laid down by William Denny and Brothers at their Dumbarton, Scotland shipyard as a fast packet for the South East and Chatham Railway's Folkestone-Boulogne run. The ship was launched on 23 September 1911 and completed later that year. She was requisitioned for service by the Admiralty on 11 August 1914, and was commissioned on 1 September after she was modified to handle seaplanes by Chatham Dockyard. Three canvas hangars were installed, one forward and two aft, and there was no flight deck, the aircraft being lowered onto the sea for takeoff and recovered again from the sea after landing by newly installed derricks. In 1918 her crew numbered 197 officers and enlisted men, including 53 aviation personnel.