A bomb is a military device that a destructive effect on a target, destroying itself in the process. The bomb may be manually placed on a target, or dropped from the air onto it (see gravity bomb and guided bomb). There is a means of triggering the effect (i.e., detonation) under conditions desired by the user of the bomb.
Moving the bomb to the target
The device does not have any type of active propulsion, either internal to it such as a rocket engine, or imparted to it externally, as by the rapid combustion of a propellant in an artillery piece. Destructive devices that are actively propelled are called warheads. Gravity bombs are dropped from aircraft.
One may manually place the bomb on the target, such as the bombs, operated by a timer, that were used in assassination attempts on Adolf Hitler e.g, by Georg Elser in 1939 and by Claus Schenk, Count von Stauffenberg in 1944). Small bombs that can be thrown by hand are usually called grenades. Explosives that are carried by the user to the target and detonated against it, with the user also receiving the usually fatal effect, include car bombs and various types of explosive-filled apparel.
Some devices are manufactured for military use that will involve manually placing it on a target, and these have various names such as demolition charge. If they are triggered by some action of the target, they are called mines or boobytraps A manually delivered bomb that is not the product of formal manufacturing is one type of improvised explosive device (IED); other types of IED are triggered by an action of the target and are also termed boobytraps.
Control of the effect
It also has a means of deciding when to trigger the effect, such as a fuze or a communications link over which a triggering signal is received (i.e., command detonation. Gravity bombs, for example, may have fuzes that act immediately on contact with the target, or delay slightly so the bomb casing can penetrate into the target. A bomb may have a proximity fuze so that it detonate at some altitude above the ground.
Before the 20th century, bombs did include externally propelled shells such as a bursting mortar shell. In the United States' national anthem, "The Star-Spangled Banner", the "bombs bursting in air" refer to shells fired from British warships in Baltimore Harbot, which exploded in the air over Fort McHentry.
The effect is most commonly explosive blast, but could be intense heat (i.e., incendiary), blast and small pieces of fast-moving metal (e.g., blast-fragmentation), or a nuclear explosion. Bombs may release chemical warfare or biological warfare agents.
Some guided bombs, do not contain any destructive material in their warhead, but still have an inert warhead filled with an inert material such as concrete. Such a warhead still has a destructive effect, as it is only used with weapons that move extremely fast, acquiring large amounts of kinetic energy. The kinetic energy of a concrete-filled bomb case will destroy that which it hits, with far less danger to adjacent people and things that if the bomb contained explosives.
Warheads on bombs traveling much more slowly may have inert fillers, or perhaps a chemical that generates smoke. Such warheads are used for training and practice.