The film takes its name from the practice of setting a small fire to clear out nearby brush, allowing a fast-advancing forest fire to pass by harmlessly.
"When they put fire retardant down on the leading edge of the fire, it's very effective in keeping the fire from advancing, " the lieutenant colonel said.
With Nazi forces advancing rapidly on the valley and British Spitfires desperately trying to draw German fire, the transport planes evacuated about 1, 000 wounded partisans in a matter of hours.