Five sisterships built for P&O's secondary one-class service to Australia. This was not a successful class, all ships having been withdrawn within 15 years. They had accommodation for 500 passengers, whilst an additional 700 temporary berths could be rigged for the outbound emigrant voyages. They sailed to Australia via Cape Town, and offered departures every two weeks. By 1926, the third class emigrant trade was collapsing, and in 1929 the route via Capetown was abandoned. The ships were refitted in turn, including conversion to oil firing, and returned to service with accommodation for 586 one-class passengers. They were used on the mail route to Australia via Suez, charging third class fares for much improved accommodation compared to their earlier history. However, their withdrawals started only seven years later.

Mongolia (3) was chartered to NZSC from 1938 as the Rimutaka, and was sold in 1950 to the Incres Shipping Company, being renamed the Europa and later the Nassau.

The ship was purchased in 1961 by Natumex Line (Compania Navegacion Turística Mexicana SA), a Mexican government-owned company, to provide a fortnightly service between Acapulco and Los Angeles. She underwent a rebuild by the Fairfield Shipbuilding & Engineering Co., Ltd. of Glasgow, Scotland including the fitting of a new bow and funnel. The Acapulco then sailed for the United States, where it initially failed inspections by the United States Coast Guard. On its third trip from California, it suffered a mechanical breakdown at sea. In 1962, she went to the Seattle World's Fair to serve as a hotel ship. In 1963, she was laid up at Manzanillo, Colima, and in 1964 Acapulco was towed to Japan for scrap, arriving at Osaka on 15 December 1964 for breaking up at Sakai. Demolition commenced on 6 January 1965.