Australia’s first naval submarine, the HMAS AE-1, has been found after a 103-year search in the 13th mission to locate it.

Using an underwater drone floating 40m (131ft) above the sea bed to scour the area, the wreck was uncovered.

On 14 September 1914, the submarine lost in World War One vanished off Rabaul, in Papua New Guinea with 35 Australian and British crewmates onboard.

The discovery solves Australia’s oldest naval mystery, the government said.

Australia’s defence minister Marise Payne said on Thursday:

This is one of the most significant discoveries in Australia’s naval maritime history.  It was the first loss for the Royal Australian Navy and the first Allied submarine loss in World War One; a significant tragedy felt by our nation and our allies.

The search team conducted a brief commemorative service for those who had lost their lives onboard.

“I truly believe this will bring peace of mind to the family and descendants of the crew who lost their lives onboard and perhaps, in time, we may discover what caused the submarine to sink,” Payne added.

Rear Admiral Briggs, president of the Submarine Institute of Australia said the discovery was “the end of that chapter, we’ve found the men of AE1, we’ve found the wreck, we’ve got some insight into its condition, and that opens the next chapter: learning exactly what happened to it, it will be quite a detective puzzle, the question of erosion in its own right, what’s happened will be an interesting challenge.”

The location of the wreck has been kept secret to prevent salvage attempts.

Australian and Papua New Guinean officials will consider how best to preserve the site and establish a lasting memorial for it.

“Bottom line (is), we have found our lost submariners, but understanding exactly what befell them is a work in progress and will require further detailed examination of the wreck with a different array of instruments and technology,” added Briggs.