The latest search for Australia's first submarine AE1 has failed to solve the mystery of the vessel's disappearance at the start of World War I.
Chairman of the Find AE1 group, retired submariner Rear Admiral Peter Briggs, said it was disappointing not to have found the boat, and her 35 Australian and British crewmen.
AE1 vanished while patrolling off East New Britain on September 14, 1914 and the latest search involved using a leased boat and special sonar to examine an area of seabed off Duke of York Island.
"Whilst it is disappointing not to have found our 35 missing submariners, we are able to conclude that their submarine does not lie intact within the 200-metre contour in the area we searched," he said in a statement on Friday.
Like many submarine losses from the two world wars, AE1 sailed out on patrol and simply never returned. There was no distress call and no witnesses, and all who might have shed any light on events sank with her.
Over the years there have been a number of searches for AE1, most recently last year when a navy minehunter found no trace of the missing vessel.
Because no wreckage, oil or bodies were found, it's thought that AE1 sank intact, most likely after striking a reef that holed the pressure hull.
The latest search started last week and over five days, the search team scanned the bottom off Duke of York Island down to a depth of 400 metres, concluding AE1 didn't sink close to the shore.
Vice Admiral Briggs said that provided an excellent starting point for the next search.
"The scene is now set for the more expensive and better resourced deep-water search that will follow. We will return to locate and solve the mystery of AE1," he said.