In 1991, during the Gulf War, she was fitted with an extensive and fully functional hospital to assume the additional role of Primary Casualty Receiving Ship.

[13] The ship was built by Società Italiana Ernesto Breda at Marghera in Italy for Contender 2 Ltd (Sea Containers, Managers) of Hamilton, Bermuda, and was launched on 28 November 1980.

By coincidence both tenders proposed converting the laid-up Contender Bezant and in March 1984, a fixed price contract was awarded to Harland and Wolff.

Having been initially designed as a container ship, she would have been too stable when unloaded, making her motion at sea "very stiff" which resulted in a very short roll period which is not appropriate for operating helicopters.

For the 1991 Gulf War Argus was fitted with a fully functional hospital, which has since been modified and extensively augmented with specialist equipment, providing 70 to 100 beds.

In 2007 the ship was refitted with upgraded hospital facilities (replacing the forward aircraft lift with a ramp for emergency exit for hospital trollies and patients as well as two 50-man passenger lifts that lead to a new structure erected on the flight deck), generators and aviation systems (the ship had been due to receive an upgrade to its night-vision capabilities enabling the use of WAH-64 Apache helicopters) to provide an operational life (at that time) until 2020.

On 2 February 1998, three helicopters based on Argus rescued 12 members of the crew of MV Delfin Mediteraneo from their life rafts when the ship sank in the Atlantic.

A project to replace Argus called the Joint Casualty Treatment Ship (JCTS) was put on hold in December 2001 after passing initial approval.

Their primary mission was to support the British Overseas Territories should they require assistance in the hurricane season as well as maintaining the constant Royal Navy presence within the wider region.

Before commencing her disaster relief mission the ship engaged in multinational exercises and celebrations commemorating the War of 1812 with units from the US Navy[26] as part of OpSail 2012.

[28][29] On 8 October 2014, UK Foreign Secretary Philip Hammond announced that the RFA Argus would travel to Sierra Leone to assist with the 2014 Ebola outbreak.

[31] Their work of establishing shore-based medical facilities and transporting aid to outlying areas earned the ship an Admiralty Board Letter of Commendation and 167 Ebola Medals for Service in West Africa were awarded to crew members.

[14] In mid-2017 Argus was host to four Wildcat helicopters from 825 Naval Air Squadron for initial training off the coast of Portugal which lasted for three weeks.

[39] In the autumn of 2023, following intensive maintenance and upgrade for her new role, the ship was expected to deploy east of Suez as the principal unit of Littoral Response Group (South).

[42] It was subsequently indicated by the Government that she was to remain, for a time, in the Eastern Mediterranean with Lyme Bay as part of a broader British regional presence given the outbreak of the 2023 Israel–Hamas war.

[49] In July 2024, both Argus and Lyme Bay deployed to Australia for exercise "Predators Run" which included troops from 40 Commando Royal Marines, and also involved US and Australian forces.