【Osawa Yuka Archives】

One of World War I's biggest mysteries has finally been solved after a 103-year search.

On Sep. 14,Osawa Yuka Archives 1914, Australia's first submarine, the HMAS AE1, disappeared off the coast of Rabaul, Papua New Guinea.

It followed a successful mission to help capture what was then known as German New Guinea, and was the first loss for what was a young Royal Australian Navy.

35 crew members went missing without a trace.

That's until an expedition this week, the 13th search for the submarine, which located the AE1 on Wednesday off the coast of the Duke of York Island group, in east Papua New Guinea.

The search vessel, Fugro Equator, found an object of interest in waters 300 metres (328 yards) deep, which was later confirmed to be the AE1. The cause of why the AE1 sank is yet to be determined.

"We can now remember and properly commemorate their service in the Australian nation," Australia's Defence Minister, Marise Payne, explained at a press conference.

"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."

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"We will work closely with the Papua New Guinea Government in the coming weeks and months to consider a lasting commemoration in recognition of the crew, and, importantly, to preserve the site."

A small commemorative service was held upon the discovery of the AE1 by those aboard the search vessel, and descendants of the crew will be notified of the finding.

"For Navy, it demonstrates the persistence of a view that fellow mariners always have — that is, we always seek to find those who have sacrificed so much for our country [so they can] actually lay to rest," said Vice Admiral Tim Barrett, from the Royal Australian Navy.

Back in October, Australian researchers found the SS Macumba, a lost merchant ship which was attacked and sunk by two Japanese aircraft in 1943 during the midst of World War II.

As for the AE1, its discovery ends the country's longest naval mystery.