(Tr: t. 290; l. 125'; b. 23'6"; dph. 12'7"; dr. 11'6" (max.); s. 10.5 k.; cpl. 19; a. small arms; cl. "Castle")
William Caldwell—a steel-hulled, coal-burning, screw steam trawler built for the British Admiralty in 1918 at Beverly, England, by Cook, Welton, and Gemmell, Ltd.—was leased to the United States Navy in the spring of 1919 for service with the North Sea Mine-sweeping Detachment which was established to clear the North Sea Mine Barrage that had been laid during World War I. She was commissioned at Grimsby, England, on 28 May 1919, Ens. Charles A. Ryan, USNRF, in command.
After arriving at Kirkwall, Scotland, the base of the detachment, on 1 June, William Caldwell got underway for the minefields on the 10th. She delivered "plunger kites" and sweep wire to the minesweepers engaged in the clearance work, followed them as they cut loose mines from their moorings, and sank the drifting mines with rifle fire. William. Caldwell returned to Kirkwall on 14 June but later shifted to the port of Thurso to load supplies. Returning to her home base on the 29th to discharge her cargo, the trawler moved to Base 18, Inverness, Scotland, at the end of the following month and remained there from 30 July to 1 August.
She next returned to Kirkwall, tended the minesweepers based there, and performed local towing duties before she towed a barge from Kirkwall to the Shet-lands. Upon her arrival at Lerwick, she delivered supplies to the tender Panther. Standing out of Lerwick on 16 August, William Caldwell ran aground on a reef near North Ronaldsay Firth, Orkney Islands, and suffered slight hull damage. Refloated at 0130 on the 17th with the use of her anchors and sweep wire to "kedge" the ship off the reefs at high tide, the trawler put into Rosyth on the 22d. There, she underwent hull repairs before she returned to Kirkwall on the 27th. William Caldwell subsequently performed additional local towing and barge-handling duties and delivered supplies during some of the final mine clearance operations in mid-to-late September.
Departing Kirkwall on 28 September, William Caldwell touched at Granton, Scotland, and Harwich, England, before arriving at Brightlingsea, England, on 3 October, in company with the converted yacht Yankton and the trawler Thomas Laundry. William Caldwell was decommissioned on 6 October 1919 and returned to the British Admiralty.