LONDON — For more than a century, the fate of Australia’s first military submarine was one of the country’s enduring maritime mysteries.

The vessel, lost off Papua New Guinea in September 1914, barely seven months after being commissioned for service, disappeared with 35 crew members during operations to capture the German Pacific colonies in World War I.

Now the puzzle is solved.

The Australian Navy announced on Thursday the discovery of a wreck they identified as the submarine, the AE1. The discovery was made by a survey ship, the Fugro Equator, that was used in another seemingly impossible endeavor: the search for the remains of Malaysia Airlines Flight 370, which disappeared during a flight from Kuala Lumpur to Beijing on March 8, 2014.

Image The underwater autonomous vehicle used in the successful search for the AE1 submarine. Credit... Bayden Findlay/Royal Australia, via European Pressphoto Agency

Images captured during the expedition suggested the submarine was well preserved and still in one piece.