Convoy GP55

USS LST-469 under repair in August 1943

Date	15–20 June 1943
Location	Australian east coast
Result	Japanese victory

Belligerents

Empire of Japan

Australia

United States

Strength

One submarine

Five corvettes
Ten cargo ships
Three LSTs

Casualties and losses

One submarine lightly damaged
One submarine possibly sunk

One transport ship sunk
one LST damaged
28 killed and 21 injured

Convoy GP55 was a convoy of Allied ships that travelled from Sydney to Brisbane in June 1943 during World War II. It comprised ten cargo ships, three landing ships, tank (LSTs) and an escort of five corvettes. The Japanese submarine I-174 attacked the convoy on 16 June, sinking the United States Army transport ship Portmar and damaging USS LST-469. Two of the corvettes counter-attacked I-174, but only lightly damaged her.

The Australian military conducted an intensive search for I-174 in the days after the attack in the mistaken belief that she had been significantly damaged. This search was not successful and highlighted the unsatisfactory communications between the Royal Australian Navy (RAN) and Royal Australian Air Force (RAAF). However, another Japanese submarine passing through the area may have been sunk by RAAF aircraft. Because of Japan's deteriorating strategic situation, I-174 was the last Imperial Japanese Navy (IJN) submarine to operate off the Australian east coast.

During 1942 and 1943, Japanese submarines periodically operated in the waters surrounding Australia. A force of midget submarines raided Sydney Harbour on the night of 31 May – 1 June 1942 and attacks on merchant shipping travelling off the east coast began several days later. These attacks continued until August 1942, when the Japanese submarine force was redeployed. The Kaidai-class submarine I-174 made a 24-day patrol off Australia in July and August 1942, but did not attack any ships. In response to the Japanese attacks, the Australian naval authorities ordered that all ships with a displacement of more than 1,200 tons and a maximum speed of less than 12 knots travel in escorted convoys from 8 June. These convoys were successful in minimising losses, and no escorted ships were sunk off Australia during 1942.

...
Wikipedia