Missile system 'no longer needed': Christopher Bellamy looks at the reasons behind cancellation of the TASM project

TRIDENT will be Britain's only nuclear weapon system from about 2006, fulfilling the 'sub-strategic' as well as strategic roles, the Government announced yesterday.

As widely predicted, the planned Tactical Air-to-Surface Missile (TASM) for the RAF has been cancelled, reflecting new political, military and technical conditions, nationally and internationally. Privately, MoD sources said that to have proceeded with a second new nuclear system in the present international climate would have been 'ridiculous'.

The decision was based on political and strategic rather than financial considerations. The cancellation of TASM, costed at pounds 1.8bn, does not help the Government in its immediate financial difficulties. The bulk of that expenditure would have fallen at the turn of the century, and continued after the last of the ageing WE-177 free-fall bombs it was due to replace had been scrapped in 2007. The Government is under pressure to make cuts over the next three years. But TASM was the only discrete, big defence equipment project remaining as a candidate for cuts in the longer term.

With the demise of the Soviet Union, and dramatic reductions in superpower nuclear arms, it appeared to many that if, as the Government believes, Britain still needed one nuclear weapons system, it certainly did not need two.

Instead, Trident will do two jobs. As the strategic deterrent, it was designed to overwhelm the most sophisticated anti-ballistic missile defences, around Moscow, with a fusillade of up to eight independently targeted warheads from each missile. The Trident force could carry up to 512 warheads - eight on each of 64 missiles in four submarines - although in practice many fewer will be deployed.

But Trident, the Government has been advised, is flexible and accurate enough to be used for a 'limited nuclear strike' - possibly with just one warhead per missile. The decision on how the missiles were to be armed would have to be taken before a Trident submarine set out on patrol, as the warheads cannot be adjusted once the submarine has put to sea. A submarine could carry missiles armed for both strategic and 'sub- strategic' strikes. The size of the explosions (the 'yield') of the British warheads is secret.

Developments in international relations and military technology combined to call into question the need for a separate, 'sub-strategic' nuclear system.

With a probable error of less than 100 metres at ranges up to 12,000 km (7,500 miles), Trident is accurate enough to deliver a precise warning to anyone threatening Britain or its essential interests - as accurate and flexible as a missile fired from an aircraft.

The 'sub-strategic' system to replace the RAF's WE-177 free-fall nuclear bombs had two possible roles. One was to deter nuclear, chemical or biological attack by 'emerging' or 'threshold' nuclear powers such as Iraq, or by former Soviet republics. Such states, it was argued, might not believe that Britain would use the full might of Trident against them, and there was always the danger that if a missile were launched, the Russians - despite the recent improvement in relations and the installation of telephone hotline between London and Moscow - would assume it was aimed at them.

A separate system, which a hostile state could see being loaded on to aircraft, and even approaching on board an aircraft, was seen as complementary, although it was always uncertain how susceptible an irrational Third World potentate was to deterrence.

The second role was to attack large military targets, command centres and bases behind forward enemy troops in eastern Europe and what was the western Soviet Union.

The changed strategic geography of Europe has reduced the number of military targets suitable for nuclear attack, but defence sources said yesterday that some work on new nuclear warheads would continue under the 'Above Ground Experimental Programme'. Computer simulation and the use of lasers now make it possible to build reliable nuclear warheads without testing, which could be banned under international agreement from 1996.