The United States Army is the primary ground force in the U.S. military. The Army was one of Umbrella's bio-weapons customers, and operated its own special weapons program relating to the handling of weaponized viruses.
Umbrella and Raccoon City
Following his recent disagreements with Umbrella executives, William Birkin offered to defect to U.S. military authorities with the G-Virus. Knowing that possession of Birkin and the G-Virus would eliminate the need to purchase bio-weapons from Umbrella, the military accepted. The U.S. government decided to send a Special Forces unit to take Birkin into custody. However, Umbrella found out about the deal and sent the Umbrella Security Service to seize the virus from Birkin, while using spies within the U.S. government to cause the Special Forces to take the wrong underground lift. Rather than arriving at the underground laboratory, they arrived at the Incineration Disposal Plant P-12A. Meanwhile, the U.S.S. secured the laboratory and shot Birkin, who injected himself with the G-Virus and caused the t-Virus to leak into Raccoon City, sparking a major outbreak.
By September 25, it apparently appeared that most of the city was in ruins filled with zombies and other unseen creatures and the Raccoon City Police Department was unable to stop them due to the sheer numbers and underestimating the creatures' abilities. That same day, the President of the United States declared that Raccoon City was to be put under quarantine and deployed the U.S. Army and Army National Guard to ensure the blockade of the city and restrict civilians from coming in and out of it. Due to the nature of the assignment, the U.S. Army was ordered not to enter the city and help the RPD, leaving the outnumbered police to fend against the zombies and evacuate civilians for themselves.
However, the U.S. Army did send two of its Special Forces units into the city, mainly to recover the G-virus. One unit was sent into the Raccoon General Hospital (which hosted an Umbrella bio-weapons and virology lab) and, based on Carlos Oliveira's observations, was wiped out by a pack of Hunter βs. Another unit was sent on a specialist operation into the Incineration Disposal Plant P-12A, where they killed and were killed by a number of T-103 Tyrants sent into the facility by Umbrella to stop them.
- In Resident Evil Outbreak, if a player decides to detonate the street infected with zombies, a scene will occur where the U.S. Army deploys an investigation unit into Raccoon City, presumably to identify the cause of the outbreak.
- Also the character Mark Wilkins from the Outbreak series was a Lieutenant colonel of the U.S. Army during the Vietnam War.
- It's possible the MPs escorting Billy to his execution are members of the Army, since they carry what is known as the Army Handgun (though it is never explained exactly how Billy obtained this weapon, this is the most logical assumption).
- Billy's handgun is called the "Army Handgun" and is a modified Colt M1911. Examining the weapon explains that it is the standard handgun of the U.S. Army, which is inaccurate. While the U.S. Marine Corps still uses the Colt, the Army has switched to the Beretta 92FS (the weapon the Samurai Edge is built around). Likely this is either a translation error, or an attempt by Capcom to differentiate between both character's handguns.
- The biographies for the original Resident Evil indicated that Albert Wesker, between 1991 and 1996, was a commissioned engineering officer in the United States Army.