Departing New York in convoy on 20 December 1917, she was 900 miles off the coast of France in January 1918, when a submarine appeared astern. , one of the ships of the convoy, fired one shot at the submarine, which was not seen again. On 9 January, after the convoy had been joined by destroyer escort in the Bay of Biscay, a submarine attacked; the convoy fired 15 shots at the boat, not seen again. "Pastores" sighted submarines again during convoy crossings in August and September.