The 1960s and 70s saw the introduction of new families of automatic weapons using smaller cartridges than the full-power rifle caliber cartridges previously in use. These weapons were called Squad Automatic Weapons (SAW). They have taken roles away from the previous medium machine guns, as well as lighter machine guns of the same caliber. However, the medium machine guns continue to be used in many of their previous roles, especially on tanks and vehicles. Often, countries field a mix of medium-caliber medium machine guns, and smaller-caliber light machine guns.