Design and construction
Stalwart was designed with a displacement of 15,000 tons, although her actual displacement was 15,500 tons. This was the largest displacement of any ship operated by the RAN to that point, except for the two Majestic class aircraft carriers and the battlecruiser HMAS Australia. Stalwart was 515 feet 6 inches (157.12 m) long overall, 458 feet (140 m) long between perpendiculars, had a beam of 67 feet 6 inches (20.57 m), and a draught of 20 feet 1 inch (6.12 m). Propulsion was provided by two 6-cylinder Scott-Sulzer diesels, which provided 7,000 horsepower (5,200 kW) to the ship's two propellers, and allowing Stalwart to sail at over 20 knots (37 km/h; 23 mph).
The size of the ship's company varies between sources: Cassells states a complement of 396, while the RAN website gives 25 officers and 392 sailors. Stalwart's armament consisted of two 40 mm Bofors anti-aircraft guns. The ship was fitted for but not with two Sea Cat missile launchers. A single helicopter was carried for utility purposes; initially, this was a Westland Wessex, although it was later replaced by a Westland Sea King. The ship's helipad was capable of receiving any helicopter flown by the RAN.
On 14 November 1974, Stalwart was present at Port Moresby for Papua New Guinean independence celebrations. On 27 December 1974, after Cyclone Tracy destroyed Darwin, Stalwart sailed from Sydney as part of the disaster relief effort Operation Navy Help Darwin. The vessel arrived on 2 January 1975, and was the only vessel to dock alongside in Darwin Harbour (the other 12 ships deployed were anchored in or outside the harbour). Stalwart remained until 30 January, during which she provided workshop and maintenance facilities, was used to provide electricity to the city, and her ship's company performed an average of 1,000 man-hours of clean-up and reconstruction work per day. She was one of the last two RAN ships to leave, and arrived back in Sydney on 6 February.
In 1980, Stalwart undertook exercises of Victoria, before visiting Newcastle for Australia Day, Hobart for the Royal Hobart Regatta, then Melbourne and Sydney before March. In May, the role of Flagship of the RAN was transferred from HMAS Melbourne to Stalwart. During September and October, the ship participated in Exercise Kangaroo 81.
Stalwart was deployed on a three-month flag-showing cruise through South-East Asia during late 1984. During this deployment, the ship visited China, Indonesia, Singapore, Hong Kong, and the Philippines
On 22 October 1985, while en route from Darwin to Indonesia, a combination of cleaning chemicals and the contents of the ship's sullage tanks caused hydrogen sulfide gas to form. 62 people had to be evacuated to Darwin by helicopter after inhaling the gas, and 3 were killed; one was posthumously awarded the Bravery Medal for his actions during the incident. In November, the ship was sent to resupply the Antarctic research station at Macquarie Island after the Australian National Antarctic Research Expedition vessel Nella Dan became beset by ice. The ship took on supplies and unloaded 85 sailors at Jervis Bay on 31 November to make room for the civilians and their equipment, before sailing to Hobart and taking on more supplies and a 41-strong relief team. She sailed on 4 December to Macquarie Island, and successfully transferred the relief team and supplies, receiving 33 men for transport back to Australia.
In late May 1986, the vessel was sent to the Solomon Islands on a disaster relief mission following heavy storms. In September, Stalwart hosted a meeting of the Cabinet of Australia.
She took part in precautionary deployments to Fiji (Operation Morris Dance) and Vanuatu during 1987 and 1988. From 15 January 1989, Stalwart began scaling down her ship's company and operations; the extra space for personnel and the superior facilities on board saw her transferred to the training squadron.
Decommissioning, civilian career, and fate
Stalwart was decommissioned on 9 March 1990 at Fleet Base East. The ship was sold to the Cyprus-based Royal Sea Ferries on 3 March 1990 for conversion into a Mediterranean cruise ship. The vessel was named MV Her Majesty M. She was later renamed MV Tara II. The ship did not enter commercial service, and on 19 February 2003, Tara II arrived at Alang, India for breaking.