The "Hotshots" killed in an Arizona wildfire in June knew they were going to die after pleas for help in their final moments went unanswered, a video showing their final transmission reveals.
All 19 of the Hotshots - firefighters from the Prescott, Arizona, were killed after the inferno overtook them as they huddled in their fire shelters.
The sobering final radio transmissions from the Hotshots indicated they knew they were all going to die, retired US Forest Service deputy chief Jim Furnish told the Arizona Republic, which first published the video.
"The sobriety of the last transmission is quite telling," he said.
"They knew. They knew that this was the end. They had to get in their shelters - that was the last gasp."
Eric Marsh, the leader of the group, told supervisors over the radio the Hotshots had been cut off by the wildfire.
"I'm here with Granite Mountain Hotshots, our escape route has been cut off.
"We are preparing a deployment site and we are burned out around ourselves in the brush and I'll give you a call when we are under the she- the shelters."
It was the group's last transmission.
Experts say that at that time the fire had entirely surrounded the 19 firefighters and that they likely knew they were going to die.
The video revealed that fire commanders overseeing the attack on the Yarnell Hill Fire didn't realise that the Granite Mountain Hotshots were even still battling the massive blaze - much less in mortal danger.
Before the last transmission, Marsh spent two minutes pleading with dispatchers to send water tankers to douse the flames in the area, asking three times for planes and helicopters to attack the fire that was surrounding them.
"Breaking in on Arizona 16, Granite Mountain Hotshots, we are in front of the flaming front," he transmitted.
"Air to ground 16, Granite Mountain, Air Attack, how do you read?"
The air-to-ground controller responsible for dispatching the air support doesn't realise the urgency of the Hotshots' situation for at least two minutes.
"OK, I was copying a little bit of that, uh conversation uh, on air to ground.
"We're - we'll do the best we can,' the dispatcher said.
"We got the type 1 helicopters ordered back in. Uh, we'll see what we can do."
The footage came from the helmet camera of a firefighter not with the Hotshots group, but his microphone recorded the radio traffic of the group's final moments.
The tragedy made it the deadliest fire in more than two decades and the most US firefighters to die fighting a wildfire since 1933.