Cruise missiles can travel at up to 550mph

They can find targets up to 1,000 miles away with guidance Earth-orbiting satellites and are capable of travelling at up to 550mph.

Current variants of the missile are 18ft long and weigh 2,650lbs.

They can carry conventional 1,000lb bombs or nuclear weapons, or clusters of smaller 'bomblets'.

They were used in the US air strikes that helped end conflict in Bosnia in 1995.

The Clinton administration also launched about two dozen missiles against Iraq in 1993 to retaliate for an assassination attempt against President Bush.

Development of the cruise missile, as we know it, has been underway since World War II.

The German V1 bomb, which caused massive destruction in London, was really the precursor for the highly sophisticated weapons inuse today.

Many modern cruise missiles, however, have a far greater range than the V1's 200 miles.

A Tomahawk cruise missile being deployed in the Gulf War

They fly at one-tenth the altitude, have radar cross-sections one hundred times smaller and are two hundred times more accurate.

And whereas the V-1, which flew a predictable course at a fixed altitude, was ultimately defeated, modern cruise missiles pose far greater challenges to air defences.

They can be launched from concealed land locations, from submarines or warships, or just as easily from merchant ships, fishing boats or even commercial airliners.

In flight they can follow erratic courses, actively evade air defences and attack their targets from unpredictable directions.

Their bodies are basically un-manned aeroplanes which can be programmed to reach a target, or can be guided, in-flight, from base.