Convoy GP55 was assembled in mid-June 1943 as one of at least 69 convoys that sailed from Sydney to Brisbane during 1943. It comprised ten cargo ships and three U.S. Navy Landing Ships, Tank (LST), and was escorted by the "Bathurst"-class corvettes (which embarked the convoy's senior officer), , , and . After departing Sydney at 8.45 am on 15 June the convoy maneuvered into five columns, with three ships in each of the centre columns and two in those at the edges. The escorts surrounded the convoy, with four sailing ahead of it and "Deloraine" to the stern. RAAF Anson and Beaufort aircraft also patrolled over the convoy at all times. U.S. Army transport "Portmar", which had been badly damaged in the Bombing of Darwin on 19 February 1942, had difficulty maintaining her position in the convoy and at times straggled behind the other ships.