Completed in October 1929 as Mid-Ocean for Furness, Withy & Co Ltd, Liverpool. 1930 renamed Castle Harbour and served as passenger tender for Bermuda & West Indies SS Co, Hamilton.

At 21.20 hours on 16 Oct 1942, U-160 fired torpedoes from the starboard side at convoy TRIN-19 50 miles east-northeast of Trinidad. One torpedo struck the Castle Harbour in station #81, which lost her bow and sank within 20 seconds and another struck 30 seconds later the Winona in station #72, which was damaged but reached Port of Spain under own power.

The Castle Harbour (Master Francis Theaker) was hit under the bridge by the torpedo, broke in two and sank so fast that most of the survivors just found themselves swimming in the water after the explosion and clung to wreckage as no boats or rafts floated off the ship. Nine crew members were lost. The master and 13 crew members (the ship was armed with one 3in, four machine guns and 16 depth charges) were picked up by the American submarine chaser USS SC-503 and landed at Port of Spain, where the master and two other seriously injured men were admitted to the hospital.