The B-1B - the original B-1A project was cancelled - went into operational use in the mid-1980s but was not used in anger until December 1998, against Iraq.

Each of the 51 aircraft in active military service cost more than $200m to build.

In the early 1990s, Congress asked questions about its poor serviceability record but the air force complained that this was mainly due to a lack of funding for maintenance.

The B-1B has a "variable-geometry" or swing-wing design: The wings are swept forwards, almost at right angles to the body, for take-off and landing and cruising. They move backwards to give greater manoeuvrability at speed.

Four turbofan jet engines, with afterburners, are each able to provide more than 30,000-lbs of thrust.

This gives it a supersonic speed, in excess of 900 mph (1,450 kph). It has an inter-continental reach without needing to refuel.

There are three internal weapons bays. These can hold up to 84, 500 lb (227 kg) bombs, or 30 cluster bombs, or 24 JDAM guided bombs. They can be reconfigured to carry a range of nuclear weapons.

There is a crew of four: A commander and co-pilot, and offensive and defensive systems officers.

The aircraft has terrain-following radar and GPS satellite navigation. The two specialists have at hand a range of electronic equipment to protect the aircraft and attack ground targets.

The B-1B has some stealth features: A smooth design and the use of radar-absorbing materials gave it an appearance on radar that is said to be only 1% of that of the older B-52 bomber, even though it is only a little shorter - at 146 feet (44.5 metres) - and weighs almost the same.

It can also tow ALE-50 decoys. When B-1Bs went into action in Kosovo, air force commanders could see Serbian SA-6 surface-to-air missile radars track the planes. When the missiles were fired, they hit the decoys and the B-1s went on to bomb their targets.