Commissioned in 1922 and 1923, the sister ships Arundel Castle and Windsor Castle were the only four-funneled merchant ships built for other than transatlantic service. Although she was among the most luxurious ships on the South Africa run, Windsor Castle catered to a less fashionable clientele than her North Atlantic contemporaries, and her accommodations were less sumptuous than those of the celebrated express liners. Nor was speed a major consideration—at least at first—and at a stately 17 knots, she could make the 6,000-mile passage in about fifteen days. In 1937, Windsor Castle and her sister ship were refitted in order to fulfill the terms of a new mail contract calling for a service speed of 20 knots, which shortened the passage by three days. The ships were lengthened 25 feet (7.5 meters), and two funnels were removed.
The reengined Windsor Castle was in service only a short time when she was requisitioned by the Royal Navy for service as a troop transport during World War II. On November 3, 1940, she was hit by German bombers off the coast of Spain. After repairs, she reentered service, but she was not so lucky the second time. On March 23, 1943, she was torpedoed in the western Mediterranean in position 37°28N, 1°10E.
