'ABF' was the designation of Allied fast troopship convoys (together with a numerical suffix) plying the route across the Indian Ocean from Aden to Bombay, India (early 1944/February 1945).

The last of the series was ABF.9 of 18/23 February 1945 with four unescorted British merchant vessels in the form of the 27,000-ton Capetown Castle, 14,982-ton Ormonde, 20,026-ton Otranto, and 23,371-ton Orion.

The career of Orion may be taken as typical of the many medium-sized ocean liners which were pressed into service in World War II as troopships. The ship’s first voyage as a troopship was to Egypt, then to Wellington, New Zealand, to collect troops for delivery to Europe. The ship departed Wellington on 6 January 1940 and sailed in convoy for Sydney, Australia, to rendezvous with her sister ship Orcades, the convoy then sailing from Australia to Egypt.

On 15 September 1941, while part of a convoy carrying troops to Singapore, Orion was following the battleship Revenge in the South Atlantic when the warship’s steering malfunctioned and she was rammed by Orion, whose bow was severely. The ship reached Cape Town, where temporary repairs were effected, and then steamed to Singapore, where more permanent repairs were completed. The Japanese were nearing Singapore at this time in the final stages of their 'E' (i) conquest of the Malay peninsula, so Orion was next used to evacuate civilians to Australia.

In October/November 1942 Orion was one of many former liners involved in 'Torch', in the process completing two voyages from the UK to to North Africa carrying more than 5,000 troops in each. In 1943 her troop-carrying capacity was increased to 7,000, and with other vessels she played a major role in the movement of US troops from the USA to the UK in the build-up for 'Overlord'.

Orion's role as a troopship was less important in Pacific operations, but the ship still ferried about 5,000 troops on each of her voyages. By the time she was released from military service in 1946, Orion had carried more 175,000 military personnel and steamed more than 380,000 miles (611500 km).