The forerunner of the machine gun was the Gatling gun, invented in 1861 CE by Richard Gatling.
It consisted of a cylinder of 6 - 10 parallel barrels that were rotated by the gunner through a crank.
Each barrel fired a single round, reloaded automatically and cooled a bit before it entered the firing position again.
Because the barrel had to be manually rotated it was not a true machine gun, nonetheless lethal.
Theoretically it could fire 20 rounds per second, though real performance was about 3 times slower.
In 1883 CE Hiram Stevens Maxim invented the first real machine gun, the Maxim gun.
It used the principle that is still used by all later machine guns,
i.e. to use the energy of the recoil of a shot to reload the next round.
It could fire 10 rounds per second in theory, 5 in practice.
The Maxim slowly replaced the Gatling and remained in use into World War I.
The early machine guns were too heavy to be carried and too cumbersome to be operated by one man.
This made them ill-suited for offense.
In defense, operated from a static position, they were very useful, one gun being worth dozens of rifles.
They could and can mow down enemies charging in closed ranks mercilessly,
a lesson that was learned much too slowly during World War I.
As technology progressed, lighter, easily portable weapons became available.
These are usually not classified as machine guns, but as submachine guns or machine pistols.
Their portability is offset by smaller magazines, prohibiting them from keeping firing for a long time.
Some true machine guns have also become lighter, though they still rank among the heaviest portable firearms.
Firing a machine gun is usually done lying down, with the gun barrel propped up by a bipod or tripod.
During firing the guns can get quite hot.
Early machine guns were cooled with water; later ones by air.
Machine guns are not as accurate as rifles, compensating with a high rate of fire.
In the early years they were used to gun down dense masses of attackers; nowadays mostly for providing suppressing fire.
War Matrix - Machine gun
Geopolitical Race 1830 CE - 1880 CE, Weapons and technology