Convoy GP55

Convoy GP55
Part of the Pacific War, World War II
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.