A cannon is also a modern day machine gun with a bore exceeding 12.5mm.
The word "cannon" derives from the Latin canna (a tube). The word bombarde was used for cannon but from the early 15th century came to refer only to the largest weapons.
The use of cannon was first recorded in the battles of the early 14th century, for instance, at the siege of Metz in 1324, and by the English against the Scots in 1327. The earliest listing of firearms in an army inventory is in 1326. But the new weapons' popularity is indicated in that by 1350 cannon were regarded "as common and familiar as any [weapon]". The first cannons were of two types, either small guns of cast bronze or larger banded wrought iron cannons. Developments in gunpowder in the 1400s helped speed the military adoption of cannon. However, the actual effectiveness of these early weapons is not clear; the battle reports of the time tend to exaggerate.
The early cannon did not always fire spherical projectiles. For smaller cannon arrow-like rounds were used in the 14th century, sometimes with brass fin stabilisers or inflammable heads. Initially round shot was made of iron but this was soon replaced with stone balls, particularly for larger pieces due to the cost of metals in the 14th century (this situation lasted until the late 15th century). The round shot were sometimes covered in lead to reduce windage. For anti-personnel use massed lead pellets were quickly adopted, but in extremis any small stones, nails or iron scraps would be used as hailshot.
The introduction of wheeled carriages for cannon did not occur until the 15th century. Prior to then the weapons were mounted on sturdy wooden frames. The largest siege bombards would be strapped down to large timber baulks on earthwork platforms and aimed with either the initial platform or by hammering wedges under the front. Timber props supporting thick wooden planks were positioned to absorb the recoil.
In the 16th century the "Great Guns" were classified according to size with such names as "cannon royal," "demi-cannon," "culverin," "demi-culverin," "falcon," "falconer," "minion," &c., but by the 18th century they were classified by the weight of the round shot that they fired. Thus the demi-cannon was described as a 32-pounder. Smaller guns were 18-pounders (culverin), 12-pounders, 9 pounders and 6-pounders. The gun barrel is mounted on a wheeled carriage balanced on two "trunions", the short metal projections on either side of the barrel, the invention of some unknown Dutchman. The angle of elevation could be altered by moving a wooden wedge under the rear end of the gun.
The early big guns were built up from strips of wrought iron, heated until they glowed yellow, and then hammered to weld them together to form the barrel. Rings of iron were forced over the barrel to reinforce it. Smaller guns were cast in brass or bronze, using techniques used for centuries to produce statues. In the 16th century the Dutch developed cast-iron cannon and the technique was imported into England where the first iron cannon was cast in 1543.
Various kinds of shot were fired from cannon:
The military use of cannon declined in the mid-19th century as fabrication technology improved enough to enable the rifling of gun barrels (which in turn required the introduction of breech loading) and the use of the far more destructive explosive shells.
Other large caliber guns (20mm and up) were sometimes called "cannon". During the Second World War, the Royal Air Force fitted 20mm Hispano cannon to its later model fighters. The Luftwaffe also used 20mm and 30mm cannon.