In WWII, it took thousands of bombs to destroy a known, fixed target. The measure used by the USA for bomb accuracy is called circular error probability, or CEP. CEP for a bomb distribution is defined to be: half of all bombs dropped fall within a distance to the target equal to the CEP. In WWII, CEP for an (unguided) bomb was more than half a mile. That is to say, that half of all bombs dropped trying to hit a point would fall inside a circle of a mile diameter, centered on the target. The other half would be dropped outside the circle; these numbers clearly represent human targetting error, along with target error caused by imperfect prediction of the bomb trajectory.
In WWII, 9000 bombs would be dropped to kill an average hard point target. Iron bombs are cheap, on the order of $3000 apiece. Still, the price of a 9000 bomb raid would be $27M; not cheap. And we must add to that the cost of the aviation gas and maintenance of the 1000 bombers it takes to carry the bombs.
And that's just the cost to the attacker. The defender would not, of course, just lose the targetted building. Collateral damage would be tremendous. In WWII this was viewed as a feature. Today we regard it as a problem because killing innocents is widely regarded as unpleasant. Some of us even think of it as manslaughter.
In Vietnam, CEP for iron bombs dropped considerably, to something like 400 feet. That's an order of magnitude, but it would still mean on the order of 100 bombs would be necessary to kill a target. That's still $300000 plus the cost of many sorties.
CEP for iron bombs has gradually decreased since Vietnam, but not much. However guided munitions were invented and refined. These munitions were accurate, but costly. For instance, cruise missiles have a CEP of perhaps 10 meters; so they are practically speaking one bomb one kill. Targetting them correctly is the problem, not killing given a proper target coordinate. But they cost on the order of $400000 a pop. So while they are better than iron bombs from the point of view of collateral damage, they are no more cost effective.
The revolution is a matter of price and performance:
It is called JDAM, the not-so-catchy acronym for Joint Direct Attack Munition, which stunned NATO generals with its accuracy during last spring's Operation Allied Force in Kosovo. "It's incredible," said Air Force Brig. Gen. Leroy Barnidge Jr., who oversaw the use of 650 JDAMs on Serbia.The CEP of JDAM is on the order of 10 meters, or 30m if its GPS isn't working. All this, for roughly $20000 (the $14k mentioned above is the cost to the manufacturer as far as I can tell; the taxpayer is paying more like $18000, and the iron bomb being converted is $3-4k).
Critics of Pentagon weapon programs, which routinely cost twice as much and perform half as well as defense contractors promise, also said they were impressed. A $14,000 JDAM kit has transformed vintage, Vietnam War-era bombs into such lethal and reliable weapons that by next year, the kit will be carried by every Air Force, Navy and Marine fighter-bomber.
One such skeptic, John Pike of the Federation of American Scientists, sees JDAM as a last-minute addition to the 20th Century's pantheon to human destruction.
"It's right up there with the machine gun and the atomic bomb," Pike said of the $4 billion program.
It takes 10 minutes to add JDAM technology to the tail section of the one-ton, Vietnam-era MK48. "It's easy to handle," said Air Force Master Sgt. William Mansey, 35, of Panama City, Fla. "You only need to tighten 12 set screws." Mansey directed the arming and loading of 18 JDAMS onto each B-2 bomber that flew roundtrip missions from Missouri to Serb targets. Only two of the 650 JDAM launches failed; they were traced to faulty wiring in the plane, not the bomb, Mansey said.
The success of JDAM is tied to the new Air Force Global Positioning System. The network of 24 satellites beamed locations so precise that they permitted B-2 Spirit bomber pilots uncommon accuracy in all weather and at night.
The JDAM bombs were released up to 15 miles from their targets, and as they fell, the satellite signals were captured by a tiny radio receiver which in turn updated a small inertial navigation system. An electric motor then moved fins on the tail assembly so the JDAM bomb moves up or down, left or right until it hones in on the precise pre-programed longitude and latitude. The system resulted in an unprecedented number of "shacks"-direct hits-program directors said.
"It will go miles in any direction," said Barnidge, of JDAM's maneuverability.
This is revolutionary price/performance. To get a kill with JDAM, only a single bomb, or two will be dropped. A raid that even ten years ago would have cost the attacker $300K costs 30K - 10% of the price. And the collateral damage is acceptable even to our modern sensibilities.
With such accuracy, it is possible and desirable to use smaller warheads. JDAM is currently used on 1000 and 2000 pound bombs; attachments for 500 pound bombs are being developed. The logical conclusion of this may already have been reached; check out this press release:
...as U.S. and coalition forces patrol the Northern and Southern No-Fly Zones over Iraq they have had to contend with Iraqis parking mobile surface-to-air missile systems in close proximity to civilian sites. The solution? [Major General David Deptula, commander of Operation Northern Watch from 1998 to 1999, said,] "I began using inert weapons -- cement bombs," Deptula said.This is just amazing. Precision bombing with no collateral damage.
"I can't use a 500-pound, high-explosive bomb against a missile launcher if it's parked within X-thousand feet of any civilian facility. But if I've got good enough precision, and I can hit it with 500 pounds of concrete, that does the trick. So we began doing that," Deptula said.
Warfare must change with capabilities like this. Without air cover, no identifiable target of any substantial value can expect to survive. There was a limit, in WWII and Vietnam, to the amount of things we could effectively destroy with bombs. That limit is now practically gone.
UPDATE - here's another news story about concrete bombs. Excerpt:
These are basically blocks of concrete shaped as bombs and painted blue to identify them as non-explosive if they are discovered still intact after the war.Blue!