A Japanese vessel that was carrying up to 1,000 Australian prisoners of war has been found in an ocean grave 80 years after being torpedoed off the Philippines.

Using a Fugro Hugin autonomous underwater vehicle (AUV), the wreck was discovered 4,000 metres beneath the waves and settles unanswered questions that families have been asked over eight decades.

All shipwrecks are tragedies, but this one was even more poignant as the vessel, Montevideo Maru, was torpedoed by a United States submarine whose crew did not realise she was carrying POWs.

 An estimated 979 Australian citizens, 850 of them soldiers, were killed when the vessel was hit, along with civilians from 13 other countries.