Designed specifically for use against tanks and mobile artillery, the bomb is guided to its target by a Global Positioning Satellite (GPS) navigation system. Unlike the other "smart" weapons used so far in Operation Allied Force, in the Gulf War or in Operation Desert Fox against Iraq, it does not need clear weather to work.
The system is carried on the US B1B long-range heavy bomber, four of which were yesterday on their way to the Balkans region from bases in different parts of the United States. The system has never before been used in combat, but proved accurate to within 10m (33 feet) of a target in trials two years ago.
Bad weather has dogged the Nato air campaign, leading to the abortion of hundreds of missions because the aircraft could not be sure of dropping their weapons accurately. The risk of causing civilian casualties in those circumstances was considered too high. On Monday, many missions were again cancelled, including RAF Harriers'. On Friday and Saturday, no manned missions were completed by any allied aircraft. Even the much-vaunted US A-10 "Warthog" anti-tank planes, which have been reported in action over the past two days, require good weather.
While Nato spokesmen areupbeat about the capabilities of cruise missiles, which are also aimed using GPS technology, the inability to fly so many manned missions has held up the campaign and left Serbian tanks and artillery in Kosovo free to roam and kill at will.
The experience of the RAF Harriers based in Italy has been particularly frustrating. Of the six nights of the campaign so far, they have flown on only two sorties when their laser-guided bombs have been dropped successfully.
General Sir Charles Guthrie, Chief of the Defence Staff, said: "We are determined, and the pilots are absolutely determined, to avoid civilian casualties if humanly possible."
Laser, infra-red or optical (TV) guidance systems need a clear sight of the target for about 90 seconds to work properly. If it is even temporarily obscured by cloud or smoke, the system could fail to "lock on".
The Paveway II laser-guided bombs, which are being used by the Harriers, in effect travel down a beam to the target from heights of 4,000 to 5,000 metres. If the beam is broken at any time, there is a risk of dropping the bomb in the wrong place. "Because of the fear of collateral damage, the pilot has got to be absolutely sure he can lock on and maintain lock," said Wing Cdr Ken Petrie, a defence analyst.
Using GPS, however, mobile targets can be picked up and tracked by radar in Awacs or other surveillance aircraft, even in zero visibility. The bombs are designed to explode 10 to 15 metres above the ground, spreading the armour-piercing fragmentation warhead over a wide area. Any tanks, guns or armoured personnel carriers in that range would be destroyed, the theory goes. Also, as the aircraft fly at 8.5km to 10km, they can attack with much less risk than even Harrier pilots.
"The other advantage of flying at those kinds of heights is the enemy gets no warning. The first thing they know about it is when this armour- piercing metal is flying around their ears and in their tanks," said Air Vice-Marshal Tony Mason."This is not the answer to Milosovic, this is not going to end the war in 24 hours. But it does bring tremendous advantages."Reuse content