Clan Forbes was built at the Greenock Dockyard Co., Greenock as one of the Cameron class of steam merchant ships for the Clan Line.

She was launched on 8 September 1938, and had her engines supplied by the firm of J G Kincaid & Co, also of Greenock.

Clan Forbes had 20 corrugated furnaces with a combined grate area of 402 square feet (37 m2) heating five single-ended forced draught boilers with a combined heating surface of 17,780 square feet (1,652 m2) that supplied superheated steam[2] at 220 lbf/in2 to a pair of three-cylinder triple-expansion steam engines.

Each reciprocating engine had a 48 inches (1.2 m) stroke; the cylinder bores were 26 inches (0.66 m) high pressure, 42 inches (1.1 m) intermediate pressure and 68 inches (1.7 m) low pressure.

Steam exhausted from the low-pressure cylinders then drove a pair of Bauer-Wach low-pressure steam turbines with double reduction gearing and Föttinger hydraulic couplings to twin propeller shafts.

Disguised as HMS Maidstone

On 16 August 1940 Clan Forbes was damaged by bombs in a Luftwaffe air raid whilst berthed at Port of Tilbury.

In November 1940 she was one of the three merchant ships that took part in Operation Collar, a convoy to supply Malta and Alexandria.

An attempt by Italian forces to intercept the ships resulted in the Battle of Cape Spartivento, after which Clan Forbes and her sister Clan Fraser continued to Malta.

She spent some of her time disguised as the submarine depot ship HMS Maidstone, having been fitted with a dummy funnel.

J G Kincaid and Company of Greenock built the four engines, whose combined power was rated at 1,370 NHP.

She was homeported in Glasgow. On the outbreak of the Second World War, she was put into service carrying vital supplies to Britain's allies and outposts.

Surviving the war, she continued in civilian service with the Clan Line, eventually serving until 1959, when she was sold for scrapping.

She arrived at Hong Kong on 6 August 1959 to be broken up.