The Australian Defence Department says a marine wreck found off the Papua New Guinea coast is likely to be a World War II Japanese submarine.
Underwater images show the wreck 55 metres below the surface in Simpson Harbour, partially buried in the harbour floor, but upright.
Imagery obtained by HMAS Gascoyne has been examined by Royal Australian Navy history personnel, who concluded the wreck was a Japanese submarine.
The Navy will work with Japanese authorities to assist in determining the wreck's identity.
The ABC reports Rabaul was the site of fierce fighting during World War II. It was Japan's key naval base for the south-western Pacific from 1942.