On this day in 1914, HMAS AE1 went out from Blanche Bay on patrol off the coast of what is now East New Britain, Papua New Guinea, working with the destroyer HMAS Parramatta in the days after the German garrison at Rabaul was taken. She was last seen in the afternoon, running on the surface, and she did not come back. Thirty-five men were aboard, under Lieutenant Commander Thomas Besant, and all of them were lost. The crew were Australian, British and New Zealand men; she was the Royal Australian Navy's first submarine and had been in service less than seven months.
The photograph below shows her on the surface in open sea, two of her crew standing on that narrow deck beside the conning tower, a destroyer low on the horizon and a larger warship trailing smoke. It is the sort of picture taken when nothing has happened yet.
Searching for her began in 1976 and went on, mission after mission, for forty-one years. She was found in December 2017, in deep water near the Duke of York Islands, on the thirteenth attempt. One hundred and three years between the last sighting and the finding. The wreck is a war grave now, and the families who kept asking finally had a place to put the question down.
The change between the early searches and 2017 is largely multibeam sonar, which sweeps a wide corridor of seabed in one pass and returns a mapped depth for every point in it, rather than a single line of soundings. It turns guesswork into a survey you can rule out and move on from. Thirty-five men, and a long patience by those who kept looking.
The 2017 survey found her in roughly 300 metres of water, after twelve earlier searches had come back empty. Deep enough that each attempt needed better sonar than the last, and someone willing to keep funding the next one. The families waited a long time for that fix.