A handout photo received on December 21, 2017, from the Royal Australian Navy shows the wreckage of Australian submarine HMAS AE1 located in waters off the Duke of York Island group in Papua New Guinea. (Royal Australian Navy/AFP/Fugro Survey)
Australia's most enduring military mystery has been solved after the wreckage of the country's first submarine was found more than a century after it vanished off Papua New Guinea, officials said Thursday.
HMAS AE1, the first of two E Class submarines built for the Royal Australian Navy, disappeared on 14 September, 1914 near the Duke of York Islands with 35 crew members from Australia, Britain and New Zealand on board.
It was the first Allied submarine loss in World War I.
AE1 was found in more than 300 metres (1,000 feet) of water after an expedition -- the 13th such search -- was launched last week using Fugro Equator, a ship also used by Australia to hunt for missing Malaysia Airlines flight MH370.
"After 103 years, Australia's oldest naval mystery has been solved," Defence Minister Marise Payne told reporters in Sydney.
"This is one of the most significant discoveries in Australia's naval maritime history... The loss of AE1 in 1914 was a tragedy for our then fledgling nation."
Payne said she hoped the discovery would help investigators establish the cause of the sinking.
Rear Admiral Peter Briggs said the most likely cause of the loss "remains a diving accident", The Australian newspaper reported.
"The submarine appears to have struck the bottom with sufficient force to dislodge the fin from its footing," it quoted Briggs as saying.
He said the vessel appeared to have suffered a "post sinking, high energy event" that would have caused the submarine to flood rapidly, probably near the surface.
The newspaper pointed to a possible torpedo explosion or the rupture of a high-pressure air cylinder.
"When the end came for the men of AE1 it would have been very fast. They may well have not known what hit them," Briggs said.
Progression of technology
A handout photo received on December 21, 2017, from the Royal Australian Navy shows the Find AE1 survey team analyzing the drop camera vision of the wreckage of Australian submarine HMAS AE1 located in waters off the Duke of York Island group in Papua New Guinea. (Royal Australian Navy/AFP/Fugro Survey)
Construction for AE1 started in 1911 and she was commissioned in Portsmouth, England in February 1914. The sub reached Sydney in May with her sister AE2.
At 55 metres long, AE1 displaced 599 tonnes and could reach a top speed of 15 knots on the surface and 10 knots when submerged. She was armed with four 18-inch torpedo tubes.
AE1 joined naval forces assigned to the capture of the German Pacific colonies and with AE2 took part in operations leading to the occupation of German New Guinea -- the northeastern part of the island of New Guinea.
On September 14, she vanished after a rendezvous off Herbertshohe -- present day Kokopo -- near the Duke of York Islands with destroyer HMAS Parramatta.
Australia's Chief of Navy, Vice Admiral Tim Barrett, said the submarine was located using a range of technologies, including a magnetometer that measures magnetic disturbances, remotely operated vehicles and a deep-drop camera.
"Each time that we searched for AE1, the progression of technology has allowed for us to learn a little bit more," he said.
Barrett said he hoped the discovery of the vessel and the lost crew would be of comfort to their descendants.
Payne said the government was working with its PNG counterparts to preserve the site and arrange for a commemoration of the sub and its crew.
The search was jointly funded by the Australian government, the Australian National Maritime Museum and two maritime history organisations.
Submarines like the AE1 came to play key roles in WWI. But the first military submersibles had taken to the seas more than a century earlier.
The first naval submarine was purported to be Turtle, a hand-cranked vessel created in the 1770s during the American Revolution.
By the end of the 19th century, the French were developing submarines that used electric motors while Britain joined the underwater race in 1901 followed by Germany in 1905.