firearm Term used usually to describe a small arm – a weapon carried and fired by one person or a small group of people. Firearms were used in Europe in the 14th century. They were, however, ineffective in close combat until c.1425, when a primitive trigger to bring a lighted match into contact with the gunpowder charge was invented. Such firearms, called matchlocks, were heavy and cumbersome, and needed a constantly lit match. The lighter flintlock (which used the spark produced by flint striking steel to ignite the powder) superseded the matchlock in the mid-17th century. During the 19th century there were great changes. In 1805, the explosive properties of mercury fulminate were discovered and, together with the percussion cap invented in 1815, it provided a surer, more efficient means of detonation. It permitted the development by 1865 of both the centre-fire cartridge (which has been the basic type of ammunition used in firearms ever since) and breech loading, not previously practicable. Another major 19th-century advance was rifling – the cutting of spiral grooves along the inside of a barrel in order to make the bullet spin in flight. During the 1830s, Samuel Colt perfected the revolver, a pistol which could fire several shots without the need to reload. By the 1880s, magazine rifles were also in use, and became more effective with the introduction of a bolt action after 1889. Development of a weapon that could fire a continuous stream of bullets began with the manually operated Gatling gun, but the first modern machine gun was the Maxim gun, invented in the 1880s, which used the recoil energy of the fired bullet to push the next round into the breech and recock the weapon. Guns of this type dominated the trench warfare of World War I. By World War II, more portable automatic weapons, such as the Bren gun and sub-machine gun, were in use. Newer developments include gas-operated rifles, firearms with several rotating barrels and extremely high rates of fire, and small firearms that use explosive bullets.