Bomb

I

Introduction

Bomb, explosive free-falling weapon that primarily uses gravity to travel from its launcher to its target. Bombs carry and disperse either a lethal or a nonlethal substance called the payload. Bombs are similar to explosive artillery shells, but bombs are dropped from the air rather than being propelled from the ground. A typical bomb has a long, streamlined form and is comprised of a steel casing containing the payload and a detonating mechanism that causes the bomb to explode. Most bombs also have small stabilizing fins at the rear. A bomb usually hangs from shackles, either in a bomb bay inside an airplane or mounted under its wing, until the pilot or bombardier triggers its release. After the bomb has fallen a preselected distance, a spinning wheel arms the bomb, readying it for detonation. A fuse detonates the bomb and can be triggered in several ways, such as by barometric pressure, a radio altimeter, a timer, or by contact with the target.

Bombs have played an important part in warfare of the last 150 years. The first bombs were dropped from airships (lighter-than-air vessels such as balloons, dirigibles and other airships) in the mid-1800s, but bombing from the air began in earnest during World War I (1914-1918). Countries began using airplanes as bombers because they were faster and less vulnerable than airships, and could bomb with greater precision. World War II (1939-1945) saw even greater use of bombing as a weapon of war. Airplanes could travel great distances and drop bombs well behind battle lines, deep into enemy territory. Bombs were first used against troops and other military targets, but as technology and the range of airplanes improved, the role of bombing expanded. During World War II, factories, cities, railroads, and bridges were bombed in an effort to weaken a country’s ability to make war. This strategy continues today.

Both smart and dumb bombs are in use today. Most bombs are “dumb,” meaning they fall where gravity takes them. Bombsights are used by high-altitude bomber aircraft to drop the bomb as close as possible to the target area. These types of bombs cost less per pound of payload than weapons such as guided missiles or artillery projectiles, but they are also much less accurate. Weapons designers have improved the accuracy of some bombs by adding pop-out wings, moveable fins, and laser seekers; these are called smart bombs. Another version of a smart bomb is a Joint Direct Attack Munition (JDAM). The JDAM is a guidance system attached to a dumb bomb. It is also known as a satellite-guided precision bomb because it is guided by an array of satellites that form part of the global positioning system. Users of smart bombs hope to knock out their targets with fewer bombs, while reducing damage to structures or injury to people near the target. Modern bombs are broadly classified as conventional (nonnuclear) bombs or nuclear (atomic or hydrogen) bombs. See also Smart Bomb.

II

Conventional Bombs

Conventional bombs can carry a variety of payloads. Bombs that carry an explosive are called general-purpose bombs. Firebombs are designed to spread fires, rather than explode their targets. Chemical bombs are filled with chemical or biological warfare agents, such as nerve gas. Cluster bombs break apart into smaller bombs when dropped. Leaflet bombs are used to drop messages over enemy territory, often to demoralize an enemy or to provide surrender instructions.

---

---

A

General-Purpose Bombs

Most bombs carry high-explosive fillers and are known as general-purpose (GP) bombs. Fillers make up as much as 50 percent of a bomb’s weight. The filler’s blast contributes most of the destructive effect, including burning and shattering buildings, people, and other targets. British GP bombs of World War II, which they called “cookies,” were large and bulky, and had relatively thin walls to carry as much explosive as possible. Smaller jet aircraft (from the 1950s onward) began carrying bombs externally under their wings, rather than within the plane in large bomb bays. As a result, later GP bombs took on a much more streamlined shape to improve accuracy and reduce drag when carried externally.

Some types of bombs first penetrate deep into the target, then explode. These are used against armored targets such as tanks or fortified buildings such as command posts. Two of the biggest conventional bombs ever used were deep penetrators developed by Britain during World War II. The “Tallboy” weighed 5,400 kg (11,900 lb) and the “Grand Slam” weighed 10,000 kg (22,000 lb). The Grand Slam’s powerful underground explosion was so massive that it became known as the earthquake bomb. Other bombs have casings designed to fragment readily, shredding into thousands of pieces that spray out in a deadly cloud. Fuel-air explosives are bombs that carry flammable liquid that is vaporized in mid-air over a target. As the flammable fuel vapor drifts down, a detonator explodes, creating a tremendous blast effect.

One of the earliest bomb fillers was trinitrotoluene (TNT), first used in 1904. Amatol is a filler that combines TNT with ammonium nitrate for a more intense explosion. Other fillers include RDX (trimethylene trinitramine or cyclonite), which has a greater shattering effect, and Torpex (TNT, cyclonite, and aluminum powder).

Smart bombs are modified general-purpose bombs that can be guided to their target. These are also sometimes known as glide bombs. Some smart bombs are fitted with a laser seeker that homes in on a laser beam focused on the target. The beam can be aimed by the plane dropping the bomb, another plane, or an operator on the ground. Other smart bombs use a TV camera mounted in the nose of the bomb to guide it to its target. The camera can locate the target as the pilot guides the bomb, or the pilot can lock on the image, and the bomb will adjust itself to keep that image in view. When the bomb drifts off target, fins steer it back on course. Recent smart bombs use the global positioning system (GPS) for guidance. GPS satellites in orbit transmit location information to the bomb, so the bomb can guide itself to a preset destination.

B

Firebombs

Firebombs (sometimes called incendiary bombs) usually consist of a carrier holding many small sticks that explode into flame. Firebombs are used to start fires over large areas, usually industrial sites. The sticks scatter loosely as the bomb falls, sprinkling a target with hundreds of fire-starters. The first incendiaries were made by Germany during World War I, but were developed too late to be used in the war. These Elektron bombs weighed only 1.0 kg (2.2 lb) and consisted of 10 percent aluminum and 90 percent magnesium with an igniter. The Thermite bombs (aluminum and iron oxide) of World War II burned at 2200° C (4000° F). Under the right conditions, incendiary bombs can start a firestorm, a self-sustaining fire that can engulf an entire city. The rising heat from the fire creates an upward draft that draws air towards the center of the fire, fueling it even more. Napalm is an antipersonnel incendiary delivered in tumbling canisters from low altitude. Consisting of jellied gasoline and additives to enhance stickiness and burning time, napalm burns at 1090° C (1990° F) for several minutes.