The first RMS Windsor Castle, along with her sister, RMS Arundel Castle, was an ocean liner laid down by the Union-Castle Line for service from the United Kingdom to South Africa. Originally laid down in 1916, their construction was held up by the First World War. They were not completed until 1922. They were the only four-stacked ocean liners built for a route other than the transatlantic. During the 1930s, Windsor and Arundel were given refits to make them look more modern. This included reducing their funnels from four to two, with new Babcock-Johnson boilers, and they both were given raked, more modern bows, which slightly increased their length. Also removed were the ships' large gantry-like davits capable of carrying six lifeboats each (like those carried on HMHS Britannic), which were replaced with the much more common Welin davits featured on liners such as RMS Titanic.
Commissioned as a troop transport in the Second World War, Windsor Castle was sunk in 1943 by a torpedo launched from a German aircraft while in the Mediterranean Sea as part of convoy KMF-11. She was hit by the torpedo at 2:30 am but did not sink until 5:25 pm, stern first, 110 miles (180 km) WNW of Algiers, Algeria. Only one crewman, Junior Engineer Officer William Ogilvie Mann, died. 2,699 troops and 289 crew were removed by the destroyers HMS Whaddon, HMS Eggesford, and HMS Douglas.