The RAF has taken delivery of £1bn worth of new spy planes to help soldiers fighting the Taliban.
The Sentinel will be the eyes in the sky for commanders tracking the enemy in southern Afghanistan.
The plane has been developed from a commercial executive jet and each one costs £200m, including training and support.
The sleek jets are packed with enough sophisticated radar to track individuals and vehicles across the whole of Helmand, the heartland of the insurgency.
The new surveillance capability will be used to counter the growing threat from roadside bombs.
"This will save precious British lives," promised Defence Equipment Minister Quentin Davies.
"Instead of just looking through a gun sight, we're able to look over the horizon."
Operating at a height of 40,000ft, sensors in a canoe-shaped pod under the fuselage can scan an area of 71,000 sq km.
"We may not have enough boots on the ground," said Group Captain Harry Kemsley, CO of No 5 Squadron.
"But this is a real force multiplier allowing us to direct our strength right to where the enemy is."
The crew of five will spend much of their time monitoring "pattern of life"; studying behaviour on the ground below and spotting any anomalies which might point to hostile activity.
The Sentinel arrives three years late, after manufacturing hold-ups, including accidental damage to radar equipment.
Because it was ordered on a fixed price contract, however, the suppliers, Raytheon, and not the taxpayer will have to meet the cost of the delay.
It joins the Nimrod - based on the world's first jetliner - and the Reaper unmanned air vehicle as part of the UK's airborne surveillance fleet.