Most of the firearms used by the armies that fought in the First World War belong to three generations.

Firearms of the first generation, such as the French Gras or the British Martin-Henry, were single shot weapons that fired black-powder rounds. These had been introduced in the 1870s, and were rendered obsolete by the introduction of smokeless powder in the 1880s.

Firearms of the second generation, like the British Lee-Metford or the German Gewehr 88, were early smokeless powder weapons. They were also provided with a magazine of some sort. These were introduced in the late 1880s and early 1890s.

Firearms of the third generation were improved versions of firearms of the second generation. Introduced in the late 1890s or early 1900s, these weapons fired ammunition that, while usually of the same caliber of second-generation weapons, was somewhat more powerful.

The leadership of the armies that fought in the First World War preferred to provide their front-line infantry units with weapons of the third generation. When they could not do that, they made do with weapons of the second generation. Providing second generation weapons with ammunition was not difficult because it was made in the same factories that produced ammunition for third generation weapons. (The difficulties of switching from the production of second-generation ammunition to third-generation ammunition were comparable to those of a present-day soft-drink factory switching from the production of Coke to Fanta. The machinery and many of the parts were the same, but the filling was somewhat different.)

As a rule, weapons of the first generation were issued to the older men who performed security duties in rear areas, doing such things as guarding prisoners-of-war, supply depots, headquarters, bridges, railway stations, and ports. As these men did not do much firing, keeping them supplied with ammunition was not at all difficult.