A former United States Marine Corp pilot, an ex-air force engineer and an air national guard member were victims in the air tanker crash that has left firefighters reeling.
The plane crashed on Thursday in the Snowy Monaro region, about 50km north east of Cooma, while fighting fires.
Coulson Aviation, the Canadian aerial firefighting company operating the plane, said the men were fallen heroes.
Captain Ian H McBeth, 44, from Great Falls, Montana, was a long-time firefighter who served in the military and the Wyoming and Montana air national guards.
He is survived by his wife Bowdie, three children Abigail, Calvin and Ella, and parents Willian and Anneliese. Captain McBeth spent his entire career flying C-130s, the model of plane that crashed while fighting fires.
First Officer Paul Clyde Hudson, 42, from Buckeye, Arizona, spent 20 years in the US Marine Corps where he was a C-130 pilot among other roles.
He received many decorations during his military career before retiring as a lieutenant colonel. First Officer Hudson is survived by his wife Noreen.
Flight Engineer Rick A DeMorgan Jr, 43, from Navarre, Florida, served in the US Air Force and spent 18 years as a flight engineer on the C-130. He had more than 4000 hours' experience as a flight engineer and nearly 2000 hours in a combat environment. He is survived by his two children Lucas and Logan, and his parents Rick Sr and Linda.
Coulson Aviation said it was committed to supporting the families of the crew members who died in the air tanker crash.
"Right now, our hearts are with the crew's family and friends, and our Coulson family suffering in the loss of these three remarkable and well-respected crew members," it said in a statement.
"The aviation industry and emergency service sector is a small community both in Australia and around the world.
"This will be deeply felt by all. We honour the amazing crews who do incredible things in dangerous circumstances supported by world-class operations.
"We are incredibly moved by the outpouring and support from those in Australia and around the world."
The cause of the crash is not immediately known.
Coulson Aviation, which has grounded its other firefighting aircraft as a precaution following the incident, said crews would return to work "in the very near future".
"We must continue to work with emergency services to protect local communities," the company said.
NSW Rural Fire Service Commissioner Shane Fitzsimmons said the state would "forever be indebted" to the sacrifice the three men made.
"It's a body blow for everyone in the firefighting fraternity, in the community of NSW and further afield," he said.
"It's a confronting and sobering reminder of the enormity of the risk and challenge associated with this fire season and all the firefighting effort that goes along with it."
Investigators from the Australian Transport Safety Bureau will travel to the Peak View crash site, near Cooma, on Friday to start collecting evidence.
The bureau expects to complete preliminary findings within a month.
The US Embassy in Canberra flew its flag at half-mast on Friday in honour of the three crew members, and was in contact with their families.
US ambassador Arthur Culvahouse said he was "deeply saddened" by the news of the fatal crash.
"The brave Americans who died near Snowy Monaro died helping Australia in its time of need," Mr Culvahouse said in a statement.
Foreign Affairs Minister Marise Payne paid tribute to the US firefighters and said she had passed on Australia's condolences to Mr Culvahouse, while Prime Minister Scott Morrison had spoken with US Secretary of State Mike Pompeo.
The three US firefighters and the three NSW firefighters who have also died battling fires this season will be remembered in a state memorial service on February 23.
- with AAP