Assigned to the Naval Overseas Transportation Service, Willimantic completed sea trials, then loaded a cargo of 6,400 tons of flour and put to sea on 14 December 1918. She transited the Panama Canal and arrived at New York City on 9 January 1919. After bunkering, she left New York on 21 January 1919 bound for Gibraltar, where she was to await further orders. Still carrying her flour, Willimantic arrived at Gibraltar on 7 February 1919, but remained there only briefly because she immediately received orders to gut underway for Fiume on the coast of the Adriatic Sea. She reached Fiume on 18 February 1919 and unloaded her flour, which was used to relieve hunger in Eastern Europe in the aftermath of World War I. After almost a month at Fiume, Willimantic left on 12 March 1919 for Gibraltar loaded only with water for ballast. From Gibraltar she proceeded to the Azores and then to New York City, where she arrived on 13 April 1919. Willimantic was decommissioned at New York on 21 April 1919. The Navy transferred her back to the US Shipping Board the same day. Once again Willimantic, she remained in the custody of the Shipping Board and its successor, the United States Maritime Commission.
United Kingdom service and loss
Early in 1942 during World War IIWillimantic was transferred to the UK MoWT, who placed her under the management of Lamport and Holt Line. In the early hours of 24 June 1942 about 700 miles southeast of Bermuda, opened fire on Willimantic with her 10.5 cm SK C/32 naval gun| deck gun. According to Willimantics Second Officer, BM Metcalf, a shell blew away Willimantics radio room and part of her chart room, killing her two radio operators. Then a shell destroyed the DEMS gun on Willimantics poop. After further shellfire the cargo ship caught fire amidships and her Master, LE Everett, gave the order to abandon ship. A shell hit the two port lifeboats as they were being lowered, destroying them. The Third Officer and an able seaman were killed and another AB suffered a shrapnel head-wound. In total six members of the ship's complement were killed. Survivors got clear of the ship in the two starboard lifeboats. U-156s commander, Werner Hartenstein, took Captain Everett prisoner, gave Second Officer Metcalf a chart and left the two surviving lifeboats under the command of Metcalf and the First Officer, M Delaney. Metcalf had his crew rig a sail and set course south-southwest for Antigua, about 800 miles away. Delaney at first headed west and then turned south. U-156 then proceeded to sink Willimantic with further shellfire. In Metcalf's boat were 16 survivors including two DEMS gunners. After six days they sighted a Norwegian motor ship, Tamerlane. Metcalf signalled her with flares and the Norwegian replied by Aldis lamp. Tamerlane rescued the occupants of Metcalf's boat and altered course to search for Delaney's boat, which Metcalf estimated to be about 20 miles north-northeast. But Tamerlane received a warning of enemy submarines in the area, and reluctantly called off the search. Seven days later Tamerlane landed Metcalf's survivors at Rio de Janeiro. In Delaney's boat were 15 survivors including one DEMS gunner. 12 days after the sinking they reached Saint Martin in the Lesser Antilles. U-156 landed Captain Everett at Lorient. He spent the rest of the war interned at Marlag und Milag Nord in northern Germany. In total 32 of Willimantics 38 complement survived.
