On June 4th Barwon en route from Melbourne to Port Kembla, and 35 miles south east of Gabo Island N.S.W. the weather being fine and clear, the time 5.35am, the vessel proceeding independant without escort, when the Officer of the watch noticed a strange vibration and a rumbling sound under number three hatch,turning to investigate this, there was suddenly a violent explosion, that rocked the ship abeam and on the starboard side.

The Chief Officer quickly altered course to port thinking Barwon was being shelled, the blast shook the ship violently, that some hatches became dislodged, it was later discovered these were struck by jagged pieces of metal from a Japanese torpedo. Course was again altered to the north west, and then to the north east, but no further attack was made and there was no sighting of the submarine.

A crew member reported sighting the the wake of the torpedo just before the explosion, and in altering course probably turned the ship directly at the enemy. If the submarine, was lying at periscope depth to observe the effects of the attack, and seeing Barwon on collision course, and a seemingly inoffensive merchant ship turning to attack, crash dived to avert a disaster. This action possibly saved Barwon from further torpedoes, as her rapid alteration of courses soon took her out of the enemy's range of vision.