He was one of the first casualties of the Great War and is part of a mystery that has remained unanswered for 100 years.
James Benjamin Thomas, 29, was on board the AE1 submarine when it disappeared off the coast of Rabaul in the then German New Guinea on September 14, 1914.
His grandson, John Thomas, 67, of Warrimoo, flew with the RAAF 10 days ago to visit the site and mark the 100-year anniversary.
Joining dignitaries and other descendants he remembered the brief and tragic life of Australia's first submarine, which vanished mysteriously in the waters of what is now Papua New Guinea, entombing with it his grandad and the 34 other officers and crew on board. The sub had travelled to the area with orders to patrol and destroy German warships and disrupt German radio shipping communications through the Pacific.
"My grandad arrived on the 7th of September [in Rabaul] and was dead seven days later."
"He was a qualified torpedo man but he never fired a shot."
Mr Thomas said "there were tears in my eyes" during parts of the whirlwind six-day visit which included two moving ceremonies to commemorate the efforts of the Australian Naval and Military Expeditionary Force during which his grandad's name was read out as part of the roll call of the crew.
"I was there in Papua New Guinea to represent his daughter, my Auntie Dot, who is still alive today at 101," he added.
"I would have loved to have known him but it wasn't to be."
The retired mechanic and his wife, Ruth, 65, were flown there and back on a RAAF Hercules with 10 other descendants, RAAF personnel and TV news crews, to be part of the ceremonies where they also laid home-made crosses with messages from Australian schoolchildren at a temporary memorial.
The Thomas family has a long history of military service.
John's father was an army engineer in World War II and fought in Singapore.
"Unfortunately my family never discussed the war. I didn't even know my grandfather died in the war.
"My father apparently threw all his medals in Sydney Harbour when he got back."
Mr Thomas said it must have been scary for his grandmother Emma who had only recently arrived from Portsmouth in England, to find the AE1 already missing at sea. She was left alone "in a strange country with two small children," Mr Thomas said.
"Luckily Grandad had organised a house for her," Mr Thomas added. She never remarried.
Some research suggests AE1 may have been fired on by an armed German steamer which then rammed and sank the surfaced submarine as it attempted to dive but Mr Thomas said he expects they may never know what happened or find the remains.
"[But] even though I don't have a spot on the ground [where he is buried] I have an idea of where he was and now I know roughly, well, within a few miles."
Mr Thomas called it a "lovely part of the world".
"Just to go there and represent the family and say to my Grandad 'Thanks for all your efforts'.
"I think for me this has given me closure," Mr Thomas said. "It will certainly stay with me for the rest of my life."
Dr Kathryn Spurling, author of The Mystery of AE1, said there was no trace of the sub, "no oil slick, no wreckage".
"The loss of the crew of AE1 would blight families for generations, but was forgotten by a nation overwhelmed by staggering fatalities on European battlefields."
An exhibition that explores the role of the Royal Australian Navy in WWI opened this month at the Australian National Maritime Museum in Darling Harbour.
