B-61 gravity bomb; this nuclear munition has been identified as one that could be modified to hit hardened underground targets.

A gravity bomb is an aircraft-delivered bomb that does not contain a guidance system and hence follows a ballistic trajectory.

Until the later half of World War II this described all aircraft bombs, and described the vast majority until the late 1980s.

Then, with the dramatically increased use of precision guided munitions, a new term was needed to separate smart bombs from those that weren't. Dumb bomb was used for a time, but many in military circles felt it sounded too trite, and eventually gravity bomb gained currency.

Special types of gravity bombs include parachute-retarded gravity bombs and nuclear gravity bombs.

External link

• The B-61 thermonuclear gravity bomb (http://www.globalsecurity.org/wmd/systems/b61.htm)