Stella Polaris—a yacht built in 1930 at Camden, N.J., by the Mathis Yacht Building Co.—was purchased by the Navy on Navy Day, 27 October 1940 from Mr. Livingston L. Short, a prominent insurance industry leader of New York, for service as a minesweeper; renamed Goldcrest. on 14 November; redesignated PYC-4 on 23 November 1940; renamed Agate on 13 December 1940; converted to naval service at Neponset, Mass., by George Lawley & Sons; and commissioned at the Boston Navy Yard on 31 January 1941, Lt. Harry A. Adams, USNR, in command.
Assigned to duty with the 15th Naval District in the Panama Canal Zone, the former yacht—now a coastal patrol vessel— departed Boston on 19 February. Along the way, she made stops at Hampton Roads and Yorktown in Virginia, Charleston in South Carolina, and at Guantanamo Bay, Cuba, before arriving at Colon in the Canal Zone on 25 April. Agate spent her entire Navy career patrolling the waters along both coasts—Atlantic and Pacific—of the Canal Zone. When cruising along the Atlantic side, she operated out of Coco Solo and, when patrolling off the Pacific end, Balboa. She continued that duty through most of World War II but appears never to have engaged enemy forces. On 12 August 1944, with about a year of hostilities to go in the war, she was detached from duty in the 15th Naval District. The yacht departed Coco Solo on that same day. Steaming via Guantanamo Bay and Charleston, she arrived at the Philadelphia Navy Yard on 1 September. On 29 September 1944, Agate was decommissioned and turned over to the Commandant, 4th Naval District, for disposal. Her name was struck from the Navy list on 14 October 1944. She was sold on 3 July 1945 through the Maritime Commission's War Shipping Administration.