Missile defence has come a long way since Ronald Reagan called for the creation of what became known as a “Star Wars” shield to protect America from a Soviet nuclear strike.

While this vision led to new confrontations with Moscow and threatened to provoke a space arms race, US scientists and engineers got on with the job of meeting their leader’s wishes.

Since 1985, when the research and development began, the US has spent or earmarked more than $124 billion (£75.4 million) on Star Wars. Nearly $8 billion has been approved for next year.

The security environment has changed and the Star Wars programme has metamorphosed into “Son of Star Wars” — less ambitious, more focused but still expensive and politically provocative.

The idea of intercepting a nuclear ballistic missile or group of missiles has been proven. The ground-based interceptors located in Alaska and California have no warheads. All they have to do is make contact with an incoming re-entry vehicle (the nuclear, chemical or biological warhead) in space. The interceptor, travelling at 7,000mph, only has to only nick the enemy warhead, exceeding 15,000mph, for the result to be an explosion of debris and dust.

There were some early test failures but the Americans are now happy that this element of the missile defence programme will work against a limited nuclear strike from a country such as North Korea.

The original Star Wars concept of a layered missile defence still applies, but the Reagan dream has been reduced to a more realistic and affordable system. This includes equipping US naval Aegis Class warships with weapons capable of knocking out enemy missiles. About 15 US destroyers and three cruisers have been fitted with Standard missiles capable of intercepting enemy rockets.

With such huge funding still being approved by Congress, US scientists have also carried out tests on an airborne laser, fitted to a modified Boeing 747, which can destroy ballistic missiles by heating them until they fail structurally. None of these systems would function without worldwide missile-tracking and radar facilities, which the Americans have been installing around the globe — notably, upgrading the early-warning site at RAF Fylingdales in North Yorkshire and deploying radar in Japan and Israel.

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