Assigned to the 1st Naval District, Cossack conducted patrols in the Boston, Massachusetts, until October 1918. Due to an urgent need for craft such as Cossack at Brest, France, an order dated 14 October 1918 went out from Washington, D.C., to Boston, directing the Commandant of the 1st Naval District to ready six section patrol boats -- USS Commodore (SP-1425), Cossack, USS War Bug (SP-1795), USS Sea Hawk (SP-2365), USS Kangaroo (SP-1284), and USS SP-729—to be shipped to France as deck cargo along with spare parts to keep them operational. However, this proposed movement appears to have been cancelled, probably because of the armistice with Germany of 11 November 1918 that ended World War I and eliminated the need for more U.S. Navy patrol craft in Europe.