SS Portmar (1919)

Portmar was a United States-flagged merchant vessel that was constructed in response to World War I, operated by a succession of companies in the interwar period, then taken up for wartime shipping in World War II.

The ship was built to Design 1013, as part of wartime orders by the United States Shipping Board (USSB). She was laid down by Northwest Steel of Portland, Oregon, with the name West Minsi. The USSB order was cancelled during construction, but Northwest Steel completed the ship for private sale. She was sold to the Green Star Line before launching in November 1919, and was assigned the name Centaurus. The freighter was sold to Nafra in 1920, then on to the Planet Steamship Company in 1923. In 1929, the ship was sold to the Calmar Steamship Company, who renamed the ship Portmar.

In late 1941, Portmar was chartered by the United States Department of War to carry supplies to the Philippines but due to the Japanese invasion of the Philippines was retained in Australia. She was used in February 1942 to carry reinforcements from Darwin for the defenders of Timor prior to the Japanese invasion. The reinforcement convoy was shadowed by Japanese planes and attacked, forcing its cancellation. Portmar returned to Darwin on 18 February, and was still in harbour the next day when Japanese carrier-based aircraft attacked the city in the first ever attack on Australia. The ship was heavily damaged, and run aground to prevent sinking.

Portmar was later refloated, towed to Sydney, repaired, purchased by the United States Army and put back into service as an Army transport. In June 1943, she sailed as part of convoy GP55. On 15 June, off Smoky Cape, Portmar and the landing ship USS LST-469 were torpedoed by the Japanese submarine I-174. Due to a highly volatile cargo, Portmar was abandoned and sank in less than ten minutes. She was the last ship lost to the Japanese submarine campaign in Australian waters.