The bodies of two Japanese sailors are to be left in the wreck of their submarine, which was involved in an attack on Sydney harbour in 1942.
The Australian government has said it will present a jar of sand from the seabed to the families of the two men.
The government has also declared the location of the wreck, 50km (31 miles) off the coast, an historic site.
The submarine was part of an operation at the height of World War II, aimed at disrupting US and Australian shipping.
Three submarines were involved in the operation, evading protective nets stretched across the entrance to Sydney harbour and sinking an Australian naval vessel, killing 19 sailors and two Britons.
Two of the submarines were damaged during the attack, and then scuttled by their crews. But a third escaped, only to be discovered on the ocean floor by amateur divers more than 60 years later.
Now elite navy divers have managed to reach the barnacle-encrusted wreck, and are convinced that the remains of its two-man crew - Lt Katsuhisa Ban and PO Mamoru Ashibe - are still on board.
They found the ladder the pair would have used to escape stowed on the outside of the vessel.
Sand gathered from close to the wreckage during the dive will now be sent to the submariners' families in Japan.
But raising the vessel and retrieving the remains has been ruled out, because of the cost and difficulty of salvage operations in the open sea.
Instead the government has declared the wreck an historic site, protected from curious divers by sonar alarms and underwater cameras.