Smart weapon

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 Germans were first to introduce PGMs in combat, with the 1,400-kg (3,100-lb) MCLOS-guidance Fritz X armored gravity ordnance, to successfully attack the Italian battleship Roma in 1943 and sink a hospital ship at Anzio, and the similarly 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 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 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.

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