As the US unleashes its opening salvo in Iraq, "smart" munitions, guided by lasers and satellite, are playing a lead role. Pentagon planners hope they will enable the US to hammer the Iraqi military while minimizing civilian casualties.
Such weapons are far more accurate than bombs guided by nothing more than gravity. In World War II, for example, it took 108 aircraft, on average, dropping 648 bombs to destroy a single target. By the time of the 2001 campaign in Afghanistan, 38 aircraft were able to hit 159 targets on the first night of bombing.
That difference tracks tremendous advances in accuracy - particularly over the past 10 years.
During the 1990s, the military developed a broad assortment of smart munitions that can be fired from safer distances and dropped in any weather conditions; they can also burrow deep underground before exploding, or even correct for wind speed while in flight. In addition, far more American planes were equipped to carry such weapons.
As a result, smart technology has taken on an increasingly important role in conflicts. During the Gulf War, smart bombs were only about a tenth of the munitions used - but they accounted for nearly 75 percent of the targets that were successfully hit, says Air Force historian Richard Hallion.
Eight years later, in the Kosovo campaign of 1999, 98 percent of munitions dropped by American planes during air attacks on Serbian forces were precision munitions.
US air units can now achieve the same results in three days as during the entire 44-day Desert Storm air campaign, says retired Rear Adm. Stephen Baker, who commanded air operations for the aircraft carrier USS Theodore Roosevelt during Desert Storm.
In the current conflict, 70 percent of the bombs are likely to be precision-guided munitions. That figure rises to 90 percent in targeting Baghdad.
"It's an extremely significant leap in capability," says Admiral Baker, now an analyst at the Center for Defense Information in Washington.
Still, as the accidental bombing of the Chinese Embassy in Belgrade by US smart bombs suggests, even the best weapons are only as good as the human intelligence that guides them.
What follows is a summary of the US smart-bomb arsenal.
These made their debut during Vietnam and were employed extensively for the first time during Desert Storm, but did not prove as effective as the postattack videos suggested. Laser-guided bombs cannot be used in cloudy, dusty, or smoky conditions, since laser seekers require a clear line of sight.
Pilots must also release the bomb within 10 miles of the target, putting them at greater risk of antiaircraft fire. Still, laser-guided bombs are the most frequently used precision-guided munition, and today's version has been upgraded with better sensors and more stable tracking.
These bombs can be used in bad weather since they rely on coordinates relayed via satellite, rather than on laser direction. GPS-guided bombs can also be launched at targets from a safer distance than laser-guided bombs. A pitfall is that readily available GPS jammers erode their effectiveness.
The military uses several such weapons:
• Joint Direct Attack Munitions (JDAM): kits convert traditional free-falling bombs into these "smart" weapons at a cost of only $21,000 per bomb. The JDAM made its combat debut during the war in Kosovo.
At the time, the B-2 stealth bomber was the only plane capable of dropping JDAMs. By the time fighting began in Afghanistan in 2001, additional planes, such as the F-15E and F/A-18, could drop them. Today, a single B-1 bomber can carry 24 JDAMs.
• Joint Standoff Weapons (JSOW): Unlike the JDAM, the JSOW is built from the start as a smart weapon. Its design includes wings that fold out and help it glide to targets from as far away as 40 miles. The plane and pilots remain safely out of harm's way. The payload of each bomb can be customized from a variety of different munitions.
• Massive Ordnance Air Blast (MOAB): This is a new munition only recently tested for the first time. At 21,000 pounds, it is the largest conventional bomb in the US arsenal - 50 percent more explosive power than the "Daisy Cutter." Both of those bombs must be dropped by parachute from a cargo plane. Once in the air, the MOAB is guided to its target by satellite signals.
These pilotless vehicles were the weapon of choice for US strikes throughout the 1990s against Iraq, Sudan, and Afghanistan. Powered by their own engines and guided by GPS and internal navigation, cruise missiles can be launched from ships and aircraft thousands of miles away.
There are currently some 1,000 cruise-missile launch pods aboard surface ships, submarines, and strategic bombers in the Persian Gulf region.
Each of the five carrier battle groups now in the region is armed with about 400 of these missiles, which cost about $1 million each. Within the last year, the US has deployed about 100 of the latest version, the tactical Tomahawk, that can loiter in the air, give commanders a view of the battlefield, and then be programmed to hit the targets it sees.
Experimental electromagnetic-burst weapons emit a strong pulse that destroys the innards of computers and other electronic devices but leaves people and buildings unharmed.
These e-bombs could be employed to disrupt Iraqi military command and control or city electrical grids. But analysts are not sure whether these weapons are yet operational. Gen. Tommy Franks, who heads US forces in the Gulf, said Mar. 6 that he didn't "know anything about" such devices.
• Sources: Global Security.org, Federation of American Scientists, Center for Defense Information, Office of the US Air Force Historian.