By Tommy H. Thomason
Monday, September 7, 2009
Why Laser-Guided Bombs
Above is bombing accuracy data from the service trials of the Vought A-7E Corsair II used to compute its CEP, Circular Error Probable, the circle within which 50% of the bombs hit when dropped one per attack. Its bombing system was probably as accurate as could be achieved with unguided Mk 80 series bombs. Even so, the actual hits relative to the target were not as close as those on the plot. They were tweaked a bit because the bombing computer was programed for a 200 millisecond delay in bomb release instead of the measured 50 millisecond delay of the bomb rack used. (For reference, the average human's reaction time to an anticipated action is about 200 milliseconds.)
The blue rectangle is an American football field. You wouldn't want to be standing in the middle of one being targeted by an A-7E dropping a 500-lb Mk 82 general purpose bomb—the lethal and effective casualty circles are shown in red. You were more likely to be killed by one bomb than not because the fragmentation/blast effect was 100% fatal in the lethal circle and fragmentation would result in 50% fatalities in the effective casualty circle. However, bunkers, tanks, buildings, and certainly bridges were a lot less likely to damaged by one bomb. It therefore might take a lot of them to do the job.
The accuracy of precision-guided weapons is far better. Theoretically, a laser-guided bomb will hit within 10 feet of the targeted point and one with GPS capability, within 40 feet. Far fewer bombs and missions were required for a given target. The requirement imposed by stealth to limit the number of bombs to those that could be carried internally was less of a penalty. The Navy benefited even more than the Air Force because of the logistics involved in resupplying an aircraft carrier with bombs and aircraft.