Hiram Maxim's invention was not the first machine gun to be produced. However, the earlier 19th Century machine guns such as the Gatling, the Gardner and the Nordenfelt all relied on multiple barrels to provide rapid fire. Maxim's gun was different - it utilised a single barrel.
It is said that Maxim was impressed by the energy given out by a rifle's recoil. Such energy, to his mind, was completely wasted, and he set about putting this force to some useful purpose.
The principle he devised was to allow the barrel to recoil a short distance when the gun fired. In simple terms, this movement acted on the lock (a sliding breech block), forcing it to the rear. As the lock went back it elongated a spring - the fusee spring -s which pulled it forward again. The rearward action removed the empty cartridge case from the chamber., ejected it and withdrew the next cartridge from the belt. The forward movement fed this cartridge into the chamber and fired it. The cycle then commenced again. The gun's mechanism first had to be cocked manually by pulling back a crank handle on the right hand side of the body, but once the trigger was pressed the lock went forward and the gun would continue to fire until the trigger was released or it ran out of ammunition.
Continuous automatic fire generated tremendous heat in the barrel and Maxim overcame this problem by encasing the barrel in a water jacket, which contained about 7.5 pints. A sound idea, but after one minute's rapid fire of about 550 rounds, the water boiled and the steam so produced could give away the gun's position. It was found that by attaching a tube to a vent in the jacket and passing this tube into a can of cold water, the steam was condensed. The water-can also provided a supply to top up the jacket -there was an estimated evaporation rate of about 1.5 pints per 1,000 rounds fired.
The gun had to be held steady, and a massive tripod mount, weighing 51lbs was designed. The gun and tripod were carried separately. The tripod had a traversing head and was equipped with a wheel operated elevation screw. On later tripods a dial, graduated in degrees, was incorporated in the mounting to enable the gun to be readily laid on a particular bearing.
Ammunition was fed into the gun by a canvas belt with brass inserts between each cartridge. The belt held 250 rounds, and passed through the feed block from right to left. One of the problems on the Western Front was keeping belts dry and clean. If wet, they tended to swell and cause the feed mechanism to jam. Mud would also clog the gun.
The machine gun was aimed, rather like a rifle, and was fitted with a foresight and a backsight. The backsight was on a stem which, when raised, was graduated to 2,900 yards. Dual sights, like a miniature surveyor's theodolite, were also issued. These enabled the gun to be laid accurately on a bearing to bring down indirect fire on fixed lines, in much the same way that an artillery piece was laid.
The machine gunner fired from a sitting position, holding two wooden grips which were fixed at the rear of the gun. Between the grips was a thumb operated trigger with a safety bar. This bar had to be lifted up before the thumb piece could be pressed. The grips were hollow. One contained a brass oil bottle, the other an oil brush.
A variety of ancillary equipment was provided with each gun. This included spare parts, spare barrel, tools, cleaning equipment, oil cans, a 2 gallon water can, night sights, aiming posts and a slide rule. On top of all this was the ammunition - 32 belts for a two-gun section was the minimum issue, and a belt in its box weighed 221bs. Reserves of 15,000 rounds were kept in the machine gun section's ammunition cart. Given this amount of kit, as well as the gun and the tripod, one can understand why six men formed the standard machine gun team.