RMS Windsor Castle was the largest passenger and cargo liner operated by the Union-Castle Line on its Cape Mail service between Britain and South Africa. Completed in 1960, the new Royal Mail Ship was notable for the high standard, if conservative, design of her public rooms in a "traditional" first class and "contemporary" tourist class configuration, which by clever arrangement, afforded both classes public rooms and open-deck areas facing forward and aft. The spacious passenger lounges and dining rooms were designed by eminent British architects. Windsor Castle was air-conditioned throughout the passenger and crew areas. Facilities included a fully equipped hospital, two outdoor swimming pools, a health spa and a theatre/cinema. A large amount of dry and refrigerated cargo space, cargo wine tanks and a specie (bullion) room, were also fitted.

The Union-Castle Line was a British shipping line that operated a fleet of passenger liners and cargo ships between Europe and Africa from 1900 to 1977. It was formed from the merger of the Union Line and Castle Shipping Line.