H.M.S. Carnarvon Castle
- Class: Armed Merchant Cruiser
- Displacement: 20,122 tons
- Dimensions: 661 x 73.5 ft.
- Machinery: Burmeister & Wain diesels, twin screw B.H.P. 20,000 = 18 knots
- Armament: 8-6 in. (8x1), 2-12 pdr. A.A. (2x1), 2-2 pdr. A.A. (2x1) guns
- Builder: Harland & Wolff, Limited, Belfast, Northern Ireland
- Launched: 1926
- Commissioned: 9 Oct 1939
- Service: Built for Union Castle Line (British flag). Southampton-South Africa service. Armed merchant cruiser, 1939-44. On 5 Dec 1940 she fought a duel with the German raider Thor, during which she was hit 27 times with the loss of 4 dead and 28 wounded. Troopship service, 1944-47.
Immigrant service to South Africa, 1947-49. Resumed normal passenger service, 1950-62. Scrapped in Japan, 1962.