Before 02:00 on 15 February 1942, "Portmar" sailed from Darwin as part of a convoy carrying reinforcements for the defenders of Timor. Also in the convoy were the transports , , and , with an escort made up of the cruiser , the destroyer , and the sloops and . "Portmar", along with "Tulagi", carried elements of the U.S. Army 148th Field Artillery while the other ships had Australian forces embarked. By 11:00, the ships had been spotted by a Japanese flying boat, which followed them for several hours before dropping bombs at around 14:00 with minimal effect. The next day, another flying boat began shadowing the convoy around 09:15, and the ships were attacked by a force of 45 Japanese aircraft two hours later. Light damage and some casualties were suffered aboard "Manua Loa", while "Portmar" was not damaged during the hour-long attack. The likelihood of further attacks and the believed imminent invasion of Timor resulted in orders to turn the convoy around received at 15:15, with all ships back at Darwin by midday on 18 February.