Bombs were seen being loaded onto the B-52s

The planes taxied down the runway at RAF Fairford in Gloucestershire just before 1000 GMT on Friday.

As they took off, a US Black Hawk helicopter circled overhead.

The huge bombers, 14 of which have been at the base since the first week of March, were expected to be taking part in the attacks on Iraq.

Campaigners in a Greenpeace hot air balloon had earlier dropped 500 anti-war leaflets over the airbase.

They said the action was not intended to disrupt the workings of the base and they had checked no flights were due at the time.

Campaigners dropped hundreds of leaflets over the airbase

"The intention was to drop leaflets about the risk to the Iraqi civilians and the hypocrisy of the United States for selling weapons in the first place," said a spokeswoman.

"We contacted the base, the police and the Civil Aviation Authority to ensure that there was no risk to the Army, personnel and those on the balloon."

Bombs were brought to RAF Fairford from Welford in Berkshire earlier in the week and were seen being loaded on to the planes on Thursday.

Peace protesters wept, held placards and said they felt "sickened" as the B-52 bombers took to the skies.

About six protesters were at the airbase where a peace camp has now been established for several weeks.

Adele Perret, 27, from Stonehouse, near Stroud, said: "It was a complete shock although we knew they were going to go out.

"I felt very sick and I was crying and phoning people because I wanted people around me.

It is an amazing sight... I hope they all come back safe Former serviceman Kevin Newman

"All we can do is pray for the people out there and for the pilots. I want peace for everybody."

A pile of letters of support and thanks was delivered to the camp by a Royal Mail van.

A small group of aircraft enthusiasts also gathered around the base as the B-52s took off.

One man, who travelled from Milton Keynes, Buckinghamshire, said the sight of the planes taking off was "awesome".

B-52 STRATOFORTRESS Crew: Five Load: 70,000 lb (31,500 kg) bombs/cruise missiles Max speed: 650 mph (1,046 km/h) Range: approx. 8,800 miles (14,160 km) Click here for full factfile

He said: "It's all a bit of an adrenaline rush and quite an emotional thing.

"Its not often you see that many together and when it's the real thing it's very different from the training."

Former serviceman Kevin Newman, 39, from Weston-super-Mare, Somerset, travelled to the base with his wife and three children last night, and slept in the car.

He said: "Its an amazing sight. The kids wanted to come up and see - I hope they all come back safe."

Tightened security

Unarmed B-52s have regularly taken off from Fairford on training exercises in recent weeks.

RAF Fairford is designated by Nato as a forward base for US warplanes, and was last used by the bombers during the 1991 Gulf War and 1999 Kosovo conflict.

B-52s were designed to carry out nuclear attacks on the former Soviet Union, but gained fame for their deadly "carpet-bombing" runs during the Vietnam war.

Security around the base has been tightened, with armed police patrolling the area and stopping and searching people.