In 1914, Australia’s first submarine disappeared somewhere off the coast of New Britain in Papua New Guinea. At the time, there was no distress call and in the subsequent retrieval missions, no wreckage was found. The 35 crew members on board – some Australian, some British, and some from New Zealand – were all missing and their story has remained a complete mystery ever since.

Now, 103 years later, the remains of the 800-tonne vessel have been found. Australian defense minister, Marise Payne, made the announcement on Tuesday.

HMAS AE1 was the first of two E class submarines gifted to the Royal Australian Navy, which was then just a fledgling organization. The journey it took from Portsmouth, England, to Sydney, Australia, was the longest transit distance taken by a sub at the time. 

A few years later, the submarine was involved in the World War One (WW1) mission to capture German New Guinea. The expedition was a success and the Germans surrendered. But the victory was tarnished by the sudden disappearance of AE1 and the 32 sailors and three officers onboard just a day later. It was September 14, 1914 and the sub had been in operation for only seven months.

According to the Royal Australian Navy, weather conditions on their final voyage were bad. Visibility was poor and, in some cases, the crew was only able to see up to five miles ahead.

Since the disaster – the first Allied submarine loss in WWI – there have been 13 separate attempts to retrieve the wreck.

Last Sunday, an expedition set off to the waters around the coast of the Duke of York Island Group in Papua New Guinea and found the sub's remains under 300 meters (984 feet) of water. The ship involved in the rescue mission is the Fugro Equator, a vessel fully equipped with the latest in advanced search technology.

We'll have to wait to find out what actually happened on that fateful day but researchers hope the find will bring an end to this century-long mystery. Retired Rear Admiral Peter Briggs, who was involved in the search, has his suspicions, believing it an accident rather than something malicious.

“The submarine appears to have struck the bottom with sufficient force to dislodge the fin from its footing, forcing it to hinge forward on its leading edge, impacting the casing,” Briggs told The Australian.

There has been a small commemorative service held and efforts are currently being made to get in touch with the descendants of the men on board.