Precision-guided munition

A precision-guided munition (PGM, smart weapon, smart munition, smart bomb) is a guided munition intended to precisely hit a specific target, to minimize collateral damage and increase lethality against intended targets. Because the damage effects of explosive weapons decrease with distance due to an inverse cube law, even modest improvements in accuracy (hence reduction in miss distance) enable a target to be attacked with fewer or smaller bombs. Thus, even if some guided bombs miss, fewer air crews are put at risk and the harm to civilians and the amount of collateral damage may be reduced. The advent of precision-guided munitions resulted in the renaming of older bombs 'unguided bombs', 'dumb bombs', or 'iron bombs'. Recognizing the difficulty of hitting moving ships during the Spanish Civil War, the Germans were first to develop steerable munitions, using radio control or wire guidance. The U.S. tested TV-guided (GB-4), semi-active radar-guided (Bat), and infrared-guided (Felix) weapons. The CBU-107 Passive Attack Weapon is an air-dropped guided bomb containing metal penetrator rods of various sizes. It was designed to attack targets where an explosive effect may be undesirable, such as fuel storage tanks or chemical weapon stockpiles in civilian areas. The Germans were first to introduce PGMs in combat, with KG 100 deploying the 1,400-kg (3,100-lb) MCLOS-guidance Fritz X armored gravity ordnance, guided by the Kehl-Straßburg radio guidance system, to successfully attack the Italian battleship Roma in 1943, and the similarly Kehl-Straßburg MCLOS-guided Henschel Hs 293 rocket-boosted glide missile (also in use since 1943, but only against lightly armored or unarmored ship targets). The closest Allied equivalents, both non-boosted gravity-ordnance designs, were the 1,000-lb (454-kg) VB-1 AZON (AZimuth ONly), used in both Europe and the CBI theater, and the US Navy's Bat, primarily used in the Pacific Theater of World War II — the Navy's Bat was more advanced than either German PGM ordnance design or the USAAF's VB-1 AZON, in that it had its own on board, autonomous radar seeker system to direct it to a target. In addition, the U.S. tested the rocket-propelled Gargoyle, which never entered service. Japanese PGMs—with the exception of the anti-ship air-launched, rocket-powered, human-piloted Ohka suicide flying bomb—did not see combat in World War II. Prior to the war, the British experimented with radio-controlled remotely guided planes laden with explosive, such as Larynx. The United States Army Air Forces used similar techniques with Operation Aphrodite, but had few successes; the German Mistel (Mistletoe) 'parasite aircraft' was no more effective, guided by the human pilot flying the single-engined fighter mounted above the unmanned, explosive-laden twin engined 'flying bomb' below it, released in the Mistel's attack dive from the fighter. The U.S. programs restarted in the Korean War. In the 1960s, the electro-optical bomb (or camera bomb) was reintroduced. They were equipped with television cameras and flare sights, by which the bomb would be steered until the flare superimposed the target. The camera bombs transmitted a 'bomb's eye view' of the target back to a controlling aircraft. An operator in this aircraft then transmitted control signals to steerable fins fitted to the bomb. Such weapons were used increasingly by the USAF in the last few years of the Vietnam War because the political climate was increasingly intolerant of civilian casualties, and because it was possible to strike difficult targets (such as bridges) effectively with a single mission; the Thanh Hoa Bridge, for instance, was attacked repeatedly with iron bombs, to no effect, only to be dropped in one mission with PGMs.