Bomb, in modern military language, a kind of ammunition usually designed to be dropped from an airplane. The term is also used for any small explosive device used by criminals or political terrorists. In earlier times, the term bomb was applied to any container filled with an explosive mixture. When Francis Scott Key wrote in “The Star-Spangled Banner" about “bombs bursting in air,” he was referring to explosive shells fired from guns.

The first use of aerial bombs in warfare occurred in 1911, when the crew of an Italian airplane dropped several small bombs on Tripoli during the Libyan War. By the end of World War I, aerial b ombardment had become a major form of attack. The first genuinely effective bombsight was invented in the United States during the 1930's by Carl L. Norden. The Norden bombsight made possible the high-altitude precision bombing used by the United States Army Air Forces during World War II. The dropping of two nuclear bombs on Japan in 1945 hastened the Japanese surrender. After the war, the leading military powers developed a variety of nuclear bombs, but only conventional bombs were used in actual warfare.

Types of Bombs

Many different shapes, sizes, and types of bombs have been used in war. The earliest and simplest were hollow spheres filled with TNT or other explosive and equipped with fuses to cause them to explode at the right moment. Later designs were cigar-shaped, with metal fins at the tail to stabilize their flight when dropped from a plane. Some weighed only four pounds (1.8 kg) while others, known as “blockbusters,” weighed two tons (1,800 kg) or more.

Guided bombs (sometimes called “smart bombs") can be directed to a target by such means as a small built-in television camera, by following a beam of laser light illuminating the target, or by navigational signals from global positioning system (GPS) satellites. Some types of general-purpose free-fall type bombs can be converted into guided bombs by being fitted with a tail section that contains an inertial navigational system, a GPS receiver, and movable tail fins. A bomb so equipped is called a joint direct attack munition (JDAM).

Armor-piercing Bombs

are made to break through the decks of ships and explode inside.

Chemical Bombs

contain smoke-producing agents or other chemicals. Such a bomb usually has a small explosive charge to shatter the case, allowing the contents to escape.

Cluster Bombs

carry many submunitions—such as grenades, mines, or small bombs—in a container designed to spread the submitions over a relatively large area.

Demolition Bombs

are large, thin-cased bombs filled with such explosives as TNT or RDX. They demolish large buildings by the blast effect of their explosions.

Depth Bombs

are designed to be dropped in the water to destroy submarines.

Fragmentation Bombs

have thick cases and break into many small pieces that fly through the air at great speed. They are most effective against persons and light equipment.

Incendiary Bombs

contain material such as magnesium or jellied gasoline (napalm) that burns fiercely. Such fires are hard to put out. Thousands of small incendiary bombs were dropped on Japanese cities in World War II to start fires.

Nuclear Bombs

produce blast, heat, and radiation through nuclear fission or fusion.