Recently the British Royal Air Force (RAF) used its 909 kg (2,000 pound) Paveway III penetrating bombs in combat for the first time. This was during an attack on ISIL (Islamic State in Iraq and the Levant) underground bunkers in Iraq when two of these smart bombs were used to destroy the entrances to some underground command bunkers. Originally designed to attack fortified aircraft shelters and underground facilities, this particular type bomb was due to be retired in a year because it had not been used.
The Paveway III series laser guided bomb entered service in 2002 and the RAF had planned to phase them out by 2017 in favor of the new Paveway IV. But with ISIL using underground bunkers (usually old Saddam era stuff captured from the army) the RAF found that the heavier Paveway III had enough penetrating power to reach and destroy this set of bunkers, or to obliterate the entrances. The 128 kg (500 pound) Paveway IV penetrating bomb had about half the penetrating power of the heavier Paveway III.
The Paveway IV was developed in Britain and is not used by the U.S. Air Force or Navy. Introduced in 2008, over a thousand 500 pound (228 kg) Paveway IVs have been dropped in combat so far. In the U.S. JDAM and other GPS-only weapons are much more popular, although some Paveway I, II, III type bombs are still used. The improvements for Paveway IV include a low explosive model (to limit collateral damage), another model has a penetrator cap (to hit underground bunkers) which is a novel feature for a 228 kg bomb. There are also improvements in the American anti-jamming technology as well as the laser seeker technology.
Laser guided bombs have been around since the late 1960s, when the U.S. developed the first weapons of this type. American bombers used laser guided bombs successfully in the final years of the Vietnam War. The technology required is not particularly difficult, although there are a lot of little things you find, from trial and error, that you need to make the weapons reliable. One problem with laser guidance is that it does not work well, if at all, when clouds, mist or smoke are in the way. It was eventually found that adding GPS helped with that problem by getting Payeway through the clouds and close enough to the target for a laser designator (on the ground or a low flying helicopter) can direct the Paveway to the target with the required accuracy.
All Paveway bombs work use the same basic kit that is attached to an unguided bomb. The 50.5 kg (111 pound) Paveway kit contains guidance electronics, computers, and battery powered winglets. But to work the carrying aircraft must have a fire control system that enables the pilot to get the GPS data (received from troops on the ground) or laser information into the Paveway equipped bomb.
Once attached to a 909 kg (one ton), 451 kg (half ton), or 128 kg (quarter ton) bomb, the Paveway can achieve precise (within a meter or less) accuracy using a laser designator. Now there is also GPS guidance to land within ten meters (31 feet) of the aiming point. The U.S. firm that manufactures the Paveway bombs, Raytheon, has produced over 250,000 kits so far, of which about twenty percent have been used in combat with great success.
Earlier versions of Paveway only had laser guidance. Britain has since added GPS to Paveway IV. While more accurate, laser guidance requires that someone on the ground or in the air be shining a laser on the target. The Paveway then homes in on the reflected laser light (of a particular frequency). GPS guided bombs can hit the target under bad weather conditions and only have to worry about jamming of the GPS satellite signal.