G meaning in Military and Defence ?

The Gatling gun is a rapid-firing multiple-barrel firearm invented in 1861 by Richard Jordan Gatling. It is an early machine gun and a forerunner of the modern electric motor-driven rotary cannon.

The Gatling gun's operation centered on a cyclic multi-barrel design which facilitated cooling and synchronized the firing-reloading sequence. As the handwheel is cranked, the barrels rotate clockwise and each barrel sequentially loads a single cartridge from a top-mounted magazine, fires off the shot when it reaches a set position (usually at 4 o'clock), then ejects the spent casing out of the left side at the bottom, after which the barrel is empty and allowed to cool until rotated back to the top position and gravity-fed another new round. This configuration eliminated the need for a single reciprocating bolt design and allowed higher rates of fire to be achieved without the barrels overheating quickly.

One of the best-known early rapid-fire firearms, the Gatling gun saw occasional use by the Union forces during the American Civil War, which was the first time it was employed in combat. It was later used in numerous military conflicts, including the Boshin War, the Anglo-Zulu War and the assault on San Juan Hill during the Spanish–American War. It was also used by the Pennsylvania militia in episodes of the Great Railroad Strike of 1877, specifically in Pittsburgh. Gatling guns were even mounted aboard ships.