In Barbara W. Tuchman's "The Guns of August," individuals who completed their mandatory military training under universal service and were aged between twenty-three and thirty-four were designated as reserves. This classification was essential for organizing the military structure during times of conflict.
When mobilization occurred, the youngest recruits reinforced the standing army units to ensure they were at full operational capacity. Meanwhile, the older classes were organized into reserve regiments to provide additional support, thus enhancing the military's readiness for war.