She was sold to the Admiralty for use as a tender in 1920, and was later deployed at HMS Dolphin, the submarine base at Gosport, taking that name.

The ship was built by Philip & Son, Kingswear, Dartmouth Harbour, Devon, England, as Yard No.407 for the Lough Swilly Steamboat Company, based in Derry under the management of John McFarland, and initially named The Aberfoyle.

[1][3] The Aberfoyle arrived in Lough Swilly, County Donegal, via Derry, in October 1912 to enter passenger service between Fahan and Rathmullen.

[5] In October 1920, enroute from Derry to the River Thames the shallow-draught vessel ran into a severe gale in the Irish Sea and, developing engine trouble, was forced to put in to Dublin for repairs.

[7] In March 1938 the vessel was renamed Dolphin and transferred to be tender to the shore base of that name, the headquarters of the Royal Navy's submarine service, at Gosport in Portsmouth Harbour.