Mohammed Emwazi [Jihadi John] was evaporated by airstrike in Raqqa in Syria.
Eight special forces soldiers 'dug in' outside Raqqa and one assembled four 'nano helicopters' with cameras fitted.
Drones were programmed to fly outside Emwazi's hideout and beamed footage to SAS HQ and US Central Command.
Until now the top-secret operation to eliminate the masked British extremist – who beheaded UK hostages Alan Henning and David Haines – was thought to have been conducted entirely from the air without any Western troops.
But The Mail on Sunday has learned that the perilous plan depended on a team of eight men from the Special Forces regiment penetrate deep inside the ISIS stronghold of Raqqa.
And the secret weapon used to identify Jihadi John was a 1lb helicopter drone launched by the soldiers.
The daring mission began in darkness on November 11 when two US Chinook helicopters skimmed low across the Syrian desert to land at an isolated spot.
Avoiding all roads, the team of soldiers drove in desert buggies 35 miles south towards Raqqa. At about 3am, they 'dug in' five miles outside the city, where they remained undetected.
The following evening, while the rest of the team were on lookout, one man assembled four 3ft nano-helicopters with infrared and night-vision cameras in the nose. They were pre-programmed to fly to Jihadi John's hideout – a six-storey building in Raqqa.
The first drone set off towards its target, then entered 'hover and stare' mode, recording the movements of ISIS suspects at a building near the Sharksa mosque.
It beamed footage by satellite back to SAS HQ in Hereford and the US Central Command in Doha, Qatar.
At 8.30pm, with the first drone low on power, a second one took over, and after another fruitless wait, it was replaced at 10pm.
But when the third suddenly shot back images of Jihadi John – real name Mohammed Emwazi – the tension in the control rooms was palpable.
A source said: 'US commanders re-tasked a Reaper drone armed with Hellfire missiles. At 11.40 a car pulled up and he got inside. The Reaper locked on to its target and Jihadi John was history. The guys were chuffed to get that maniac.
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