Key Facts
- Date of attack
- 16 June 1943
- Convoy size
- 10 cargo ships, 3 LSTs, 5 corvette escorts
- Ships sunk
- 1 (USAT Portmar)
- Ships damaged
- 1 (USS LST-469)
- Attacking submarine
- Japanese submarine I-174
- Historical significance
- Last IJN submarine to operate off Australia's east coast
Strategic Narrative Overview
On 16 June 1943, Japanese submarine I-174 attacked the convoy, sinking the US Army transport Portmar and damaging USS LST-469. Two escorting corvettes counter-attacked I-174 but inflicted only minor damage. The Australian military, believing I-174 was critically damaged, launched an intensive multi-day search that ultimately failed to locate her. The operation revealed poor coordination between the Royal Australian Navy and the Royal Australian Air Force in anti-submarine communications.
01 / The Origins
During World War II, Allied shipping along the Australian east coast required convoy protection against Japanese submarine operations. In June 1943, Convoy GP55 was assembled to transport cargo and landing ships from Sydney to Brisbane, escorted by five corvettes. Japan's submarine force remained active in Australian waters, and I-174 was tasked with disrupting Allied supply lines in the region as part of broader IJN operations in the Pacific theatre.
03 / The Outcome
I-174 escaped and the Allied search was unsuccessful. A separate Japanese submarine passing through the area may have been sunk by RAAF aircraft. Due to Japan's worsening strategic position in the Pacific, I-174's attack proved to be the final IJN submarine operation off Australia's eastern coast. The episode prompted reflection on inter-service communication deficiencies between the RAN and RAAF, though no immediate structural reform is recorded in the source.
Belligerents & Mobilization Analysis
Side A
1 belligerent
Side B
1 belligerent
Kinetic Engagement Axis
Scroll horizontally to view full axis. Events plotted relatively.