A weapon is a tool used either in hunting, or attack or defence in combat for the purpose of subduing enemy personnel, or to destroy enemy weapons, equipment and defensive structures through application of force. A weapon is therefore a mechanical device that changes the direction or magnitude of a force. In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force.
In attack, weapons may be used to threaten by direct contact or by use of projectiles. Weapons can be as simple as a club, or as complex as an intercontinental ballistic missile. Metaphorically anything capable of being used to damage, even psychologically, can be referred to as a weapon. More recently, development of non-lethal weapon systems has been adopted for para-military, security and even combat use, designed to incapacitate personnel and reduce collateral damage to property and environment.
Very simple weapon use has been seen in some communities of chimpanzees. Craig Stanford, a primatologist and professor of anthropology at the University of Southern California, has suggested that the discovery of spear use by chimpanzees probably means that early humans used wooden spears as well, perhaps five million years ago.
The earliest and most primitive weapons were the by-products of early human hunting – claws, teeth and horns of hunted animals, shaped or adapted for use as weapons. Stone axes were used as weapons very early in human history as personal weapons of direct attack, and as a particular type of simple tool that made up for comparative lack of natural weapons, such as claws, horns and teeth, in the human physiology.
The first human use of weapons is not easy to date, as these would probably have been wooden clubs, spears and unshaped stones thrown at prey or enemy—and none of these would leave an unambiguous record.
The earliest examples found are a cache of eight wooden throwing spears, the Schöninger Speere, which have been dated as 400,000 years ago.
By 250,000 years ago wooden spears were made with fire-hardened points. From 80,000 years ago humans began to make complex stone blades, which were used as spear points.
Bows and arrows may have been used by 60,000 years ago
The Medieval period, including the Western Middle Ages, was characterized by two iconic Medieval weapons: knights, heavily-armored horsemen, and the rudimentary siege artillery to negate the increased use of castles, fortified dwellings which proliferated throughout Europe and the near east. While knights were an evolutionary development of the earlier historical cavalry such as the Roman and Persian cataphracts, siege artillery used to breach castle walls triggered quite revolutionary advances, including increasingly sophisticated siegecraft using gunpowder weapons, the cannon.
Firearms are qualitatively different from earlier weapons because they store energy in a combustible propellant such as gunpowder, rather than in a weight or spring. This energy is released quite rapidly, and can be restored without much effort by the user, so that even early firearms such as the arquebus were much more powerful than human-powered weapons. They became increasingly important and effective during the 16th century to 19th century, with progressive improvements in ignition mechanisms followed by revolutionary changes in ammunition handling and propellant. During the U.S. Civil War various technologies including the machine gun and ironclad warship emerged that would be recognizable and useful military weapons today, particularly in lower-technology conflicts. In the 19th century warship propulsion changed from sail power to fossil fuel-powered steam engines.
The age of edged weapons ended abruptly just before World War I with rifled artillery, such as howitzers which were able to destroy any masonry fortress, as well as destroy other fortifications. This single invention caused a revolution in military affairs and doctrines that continues to this day. See Technology during World War I for a detailed discussion.
An important feature of industrial age warfare was technological escalation - an innovation could, and would, be rapidly matched by copying it, and often with yet another innovation to counter it. The technological escalation during World War I was profound, producing armed aircraft and tanks.
This continued in the period between the end of that war and the next, with continuous improvements of all weapons by all major powers. Many modern military weapons, particularly ground-based ones, are relatively minor improvements on those of World War II. See military technology during World War II for a detailed discussion.
From the American Revolution through the beginning of the 20th century, human-powered weapons were finally excluded from the battlefield for the most part. Sometimes referred to as the "Age of Rifles, this period was characterized by the development of firearms for infantry and cannons for support, as well as the beginnings of mechanized weapons such as the machine gun, the tank and above all the wide introduction of aircraft into warfare, including naval warfare with the introduction of the aircraft carriers. World War I marked the entry of fully industrialized warfare, and weapons were developed quickly to meet wartime needs. Above all it promosed to the military commanders the independence from the horse and the resurgence in manoeuvre warfare through extensive use of motor vehicles. The changes that these military technologies underwent before and during the Second World War were evolutionary, but defined the development for the rest of the century. World War II however, perhaps marked the most frantic period of weapons development in the history of humanity. Massive numbers of new designs and concepts were fielded, and all existing technologies were improved between 1939 and 1945. The most powerful weapon invented during this period was the atomic bomb.
The most notable development in weaponry since World War II has been the combination and further development of two weapons first used in it—nuclear weapons and the ballistic missile, leading to its ultimate configuration: the ICBM. The mutual possession of these by the United States and the Soviet Union ensured that either nation could inflict terrible damage on the other; so terrible, in fact, that neither nation was willing to instigate direct, all-out war with the other (a phenomenon known as Mutually Assured Destruction). The indiscriminate nature of the destruction has made nuclear-tipped missiles essentially useless for the smaller wars fought since. However computer-guided weaponry of all kinds, from precision-guided munitions (or "smart bombs") to computer-aimed tank rounds, has greatly increased weaponry's accuracy.
Being able to prepare, maneuver and attack before the enemy can detect the threat and respond can be a decisive advantage. The element of surprise has long been recognized as a tactical advantage. Mondern technology can increase this, such as when one side has sophisticated night vision technology allowing maneuvering and combat at night when the enemy, not so equipped, is limited. High tech surveillance and intelligence gathering methods such as pilotless drones can prevent surprise or identify targets. Coordination of forces is necessary in order to utilize separated forces effectively, modern communications, if unjammed and unintercepted are substantial advantages. Even once targets or strategic objectives are identified, it is necessary to prepare detailed plans for individual forces to follow, a time consuming process that modern armies are trying to computerize to achieve an advantage of speed over the enemy.
Since interfering with enemy infrastructure, intelligence and communications yields an advantage, and a weapon is defined as something that grants such an advantage, new targets and weapons such as cyberwarfare are becoming possible.
Who uses it essentially determines how it can be employed:
How it works refers to the construction of the weapon and how it operates:
What it targets refers to what type of target the weapon is designed to attack: