That's the conclusion of a report from the expeditionary team that found the wreck of HMAS AE1 last December, as reported on Divernet.

AE1 was the first Allied submarine to be lost during WW1, the sinking occurring on 14 September, 1914. The wreck was discovered at a depth of 300m near PNG's Duke of York Islands.

Australia’s Minister for Defence Marise Payne has now announced that the images collected showed that the vessel’s guard-rails were stowed and that the hatches appeared to be shut.

“These first assessments from the expedition indicate that the AE1 was configured to be in a state for underwater operations,” said Payne.

“The report indicates that the AE1 was probably submerged or diving while she was returning to Rabaul [capital of the island of New Britain], after a patrol looking for enemy activity around the Duke of York Islands, when tragedy struck.

“The work undertaken by Find AE1 Limited and Silentworld Foundation to search for and locate the AE1 fills an important gap in what was one of our most enduring naval mysteries of the First World War.

"Through the tireless efforts of many, we have discovered the final resting place of the 35 souls who gave everything in service to the Allied cause.

“We are pleased to be able to provide closure for the families and the entire Navy community by identifying the resting place of the lost shipmates.”

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