She was a multi-purpose, roll-on/roll-off heavy lift ship capable of transporting soldiers, APCs, and tanks, and delivering them to shore via landing craft or directly by beaching.

The ship experienced problems during her early career with her engines (which differed from the British base design) and sewage system (leading to the death of a cadet in 1981).

During the 1980s, the ship delivered supplies to the Multinational Force and Observers on the Sinai Peninsula, assisted in the withdrawal from RAAF Base Butterworth, provided support and accommodation for delegates to the South Pacific Forum, and was part of the Australian response to the 1987 Fijian coups d'état.

Attempts to sell the ship to the British and the Portuguese did not succeed, and in 1997 the decision was made to keep Tobruk, as the Kanimblas could not completely replace the heavy lift capability provided.

After spending several months in 2010 undergoing extended maintenance, Tobruk participated in the United States Navy's Pacific Partnership humanitarian assistance deployment.

As the two Kanimblas had been forced out of service by ongoing issues, the Australian government had to charter a succession of civilian ships to provide standby heavy transport capability.

[3] Two designs were considered for Tobruk, with a modified Sir- or Round Table-class landing ship logistics, in use with the Royal Fleet Auxiliary at the time, selected for construction.

[12] Additional cargo handling was provided by the 70-tonne Velle heavy lift derrick (a feature singled out for attention in Jane's Fighting Ships), supplemented by two 8.5-tonne Favco cranes.

[5][10] Two Naval Lighterage Equipment pontoons could be carried on the ship's flanks to extend the reach of the bow ramp when beaching, or as rafts to transport cargo ashore.

[5][14] The ship left the dockyard for the first time in December 1980: her construction had been delayed by over four months by industrial disputes, and her final cost of A$59 million was 42 percent greater than originally estimated.

[18] The ship undertook its first tasking in the spring of 1981 when she transported elements of the 16th Air Defence Regiment, Royal Australian Artillery from Adelaide to Port Alma, Queensland.

[19] The cadet's death led to an inquiry into the ship by the Commonwealth Government's Auditor General which concluded that she should not have been accepted by the RAN at the time she was commissioned due to the number of defects still present.

In February 1984, Tobruk took part in exercises in New Zealand, before travelling to Tuvalu in August, where she provided support and accommodation for delegates to the South Pacific Forum.

By this time it had become clear that there would not be a need to evacuate Australians from Fiji, and Tobruk proceeded to support the South Pacific Forum meeting at Apia, Samoa after cross-decking the troops and their supplies to the other ships.

She travelled to New Zealand on a training cruise in early 1988 and was placed on alert to carry an Army force to evacuate Australian civilians from Vanuatu in April 1988 following a political crisis there.

On 26 January 1990, she was tasked to assist with evacuating Australian citizens from Bougainville in Papua New Guinea; this operation was cancelled in early February while the ship was travelling to the island from Sydney.

[28] She spent the next few days at anchor, during which she was used as a training platform for boarding and seizure operations by the United States Navy SEALs, in their preparation for the arrival of a merchant vessel smuggling weapons.

During this period Tobruk remained in active service, and in 1997 the new Liberal Party government decided to retain her until 2010 as the two LSTs could not fully replace her ability to carry heavy equipment.

The ship made six further voyages between Darwin and East Timor in September and October 1999, and continued to make an important contribution to the peacekeeping operation until November, when she returned to Sydney for maintenance.

[38] In April 2005, HMAS Tobruk left Sydney to transport 20 ASLAVs to Kuwait, where they would equip the Australian Army's Al Muthanna Task Group in Iraq.

[40] Tobruk travelled to Nias Island in Indonesia in March 2006 to support ceremonies commemorating the anniversary of the crash of an RAN Sea King helicopter there on 2 April 2005.

Following this deployment, she took part in Exercise Croix du Sud off New Caledonia, then proceeded to the Philippines where she was to embark a North American Rockwell OV-10 Bronco aircraft destined for the Australian War Memorial.

[41] In mid-May, Tobruk was recalled from her voyage to the Philippines to embark elements of the 3rd Brigade for an urgent deployment to East Timor following fighting caused by unrest in the country's military.

After unloading her cargo, Tobruk returned to Townsville where she embarked a second load of vehicles and supplies for the Australian forces in East Timor, arriving back at Dili in the first week of June.

[43] In November 2006 it was reported that while the Department of Defence had engaged a specialist to supervise the removal of large quantities of asbestos from Tobruk, her crew were concerned that the ship was continuing operations during the overhaul.

[44] In late December 2007, two groups of 60 Australian Navy Cadets and staff were embarked aboard Tobruk for the final part of the ship's deployment with Operation Resolute and the return voyage from Darwin to Sydney.

During this operation she provided medical treatment to people wounded in the blast and her embarked Sea King helicopter flew the more badly injured to Mungalalu Truscott Airbase.

[59] Following the 2011 Tōhoku earthquake and tsunami on 11 March 2011, Tobruk and Sydney were placed on alert to transport supplies and Australian Army engineers to Japan if this was requested by the Japanese Government.

[26][69] That day Prime Minister Tony Abbott, Leader of the Opposition Bill Shorten and Speaker of the House of Representatives Bronwyn Bishop made statements in parliament acknowledging the ship's service.

Federal Member of Parliament Keith Pitt spent several years campaigning for the scuttling of a warship in Hervey Bay as a tourist attraction, with Tobruk his preferred vessel.