1944: 4-Man Fire Team

As a relatively small force, Marines have always had to be more adaptable than other military branches. In 1944, to increase the combat power of their rifle squads, the Marine Corps began using 13-man squads consisting of a squad leader and three 4-man fire teams. The new formation proved more flexible than the previous 12-man squad, which lacked subdivisions. 
 
Each fire team was led by a corporal, and included two riflemen carrying M1 Garands, as well as an automatic rifleman with the Browning Automatic Rifle. The rifle squad leader may use one or two of these teams to fire, while another team maneuvered to gain ground. 
 
This efficient, high-firepower tactic was used successfully in World War II, and its core strategy is still used today.