(Tr: t. 269; 1. 125'5"; dph. 12'7"; s. 10 k.; cl. “Castle”
Thomas Blackhorne (sometimes spelled Thomas Blackhorn)—a steel-hulled steam screw trawler built for the British Admiralty in 1917 at Beverley, England, by Cook, Welton, and Gemmell, Ltd.—was leased by the United States Navy in mid-May 1919 for service with the North Sea Minesweeping Detachment and delivered to the Navy at Falmouth, England, where she was commissioned, probably on 16 May 1919.
By July 1919, Thomas Blackhorne was no longer involved in active minesweeping operations in the North Sea Mine Barrage fields but was engaged in a support role at the detachment's base at Kirkwall, Scotland. There, she provided sweep wire and stores to the minesweepers based at Kirkwall. She interrupted this duty in early August to steam out to the minefield to recover marker buoys from 4 to 8 August. She then returned to resume her local operations.
Drydocked at Wick to receive a new propeller on 16 September, Thomas Blackhorne returned to Kirkwall on the following day to operate between Inverness, Invergordon, and Kirkwall for the remainder of her active career under the stars and stripes. Early in October, she towed the disabled subchaser SC-38 (which had been damaged in a mine explosion on 25 September) to Harwich, England.
Shifting to Brighton, England, on the 5th, Thomas Blackhorne was decommissioned and returned to the Admiralty on the afternoon of 6 October 1919.