Army Rangers are a Special Forces of the United States Army. They are a United States commando unit that serve as forward troops in the most dangerous combat zones. They are experts in tactical deployment and survival.
Stargate Command employs those from this elite task force to supplement its SG teams when extra firepower and combat training are required for a dangerous mission. They also served deep in combat zones occupied by the Goa'uld. (RPG: "Roleplaying Game")