The United States National Guard, commonly known as simply the National Guard, are a reserve military unit that served to protect individual states in the United States of America. The National Guard were usually, but not always, called upon during terrorist crises.
In October 14, 2004, the National Guard was under the command of Colonel Stevens, when Gunnison, Colorado was being infested with Xenomorphs. Stevens sent several squads of National Guard personnel to the town, supported by several HMMWVs and APCs. However, the entire complement was quickly killed by the Xenomorphs. Stevens then ordered for the town to be destroyed by a nuclear strike.
The National Guard was responsible for obtaining the first recorded image of the Xenomorphs, which was recorded by a helmet camera from one of the soldiers, before he was killed by the Xenomorphs. The image was retrieved by Colonel Stevens, who presumably turned it over Ms. Yutani along with the Plasma Pistol he recovered from the incident.