By 2077, the U.S. Armed Forces were the world's most powerful military force. The only rival was the People's Liberation Army of China, with which the Armed Forces clashed during the Sino-American War, both in the Alaskan campaign (which included Anchorage) and numerous offensive campaigns waged in China.
The Armed Forces were primarily using energy weapons (laser and plasma) in the field, although due to slow production rates, many troops, in particular on the Anchorage Front Line, were still using regular firearms (such as the R91 assault rifle). Regular infantrymen, regardless of specialization, wore polymer combat armor (Anchorage troops used special winterized versions), while suits of power armor were reserved for Mechanized Cavalry units and special detachments (e.g. Colonel Spindel's group at Mariposa).
In a supportive role, the Army deployed robots―Sentry bots and combat versions of the popular Mister Handy―Mister Gutsy. Aerial support was to be provided by next-generation helicopters, the VB-02 Vertibirds, though they were scheduled to enter service in 2083, prototypes may have seen combat at Anchorage.
Fighter support was common and many patrolled the U.S. coastline and its national waters.
The first application of the United States army in the Resource Wars was a year before they de-facto began, starting with the subjugation of Mexico in 2051. Army units were being deployed in Alaska at higher levels than before following the establishment of the Anchorage Frontline in 2059. Much more veritable quantities of troops were transported to the state after the Chinese invasion of Alaska in the winter of 2066 and 2067. The United States Army was utilized in the 2072-2076 annexation process of Canada, and were decisive in defeating the Canadian military and suppressing resistance movements. Later on, in the Sino-American War, Army units were deployed in China proper and its annexed territories with the USMC following the invasion of the supra in 2074.
The Marine Corps served as the spearhead of the American counterinvasion of China during the war, due to their specialization in amphibious operations.
The only known remaining Naval ship of the United States Navy is the Aircraft Carrier used as a settlement known as Rivet City. Located on the East Coast in Washington D.C. The U.S. Navy was also deployed during the Anchorage Reclamation, as two vessels, USS Ebon Atoll and USS Interference, are mentioned in Fallout 3. There is also a Naval Recruiting Center in Point Lookout.
The National Guard were a reserve branch of the Army and primarily served as a domestic defense and disaster relief force during peacetime. However, they could be and often were deployed abroad as front-line troops in wartime. In the months and years immediately succeeding the Great War, remnants of the National Guard attempted to retain order and law in the United States, assisted by civilian elements such as nurses, and potentially police, as was seen in Germantown. However, due to the high attrition rate suffered as a result of the radiation and anarchy, most, if not all, National Guard units were whittled down by mortalities, along with desertion, and eventually disbanded.
- By far, the most notable operation is the Anchorage Reclamation, an 11-year campaign to liberate Alaska from the Chinese invaders. Ultimately successful, it was the first large-scale deployment of newly developed T-51b power armor units.
- The annexation of Canada was also performed by the United States military, whose units were also dedicated to keeping the peace―by any means necessary.
- Veterans of the Anchorage campaign were also deployed against their fellow countrymen, to contain food riots.
- The Gobi Campaign, where the U.S. attempted to capture Chinese military facilities in the Gobi Desert. The Gobi Campaign scout rifle was designed for this campaign.
- The Yangtze Campaign, during which Nanjing and Shanghai were occupied by Marines equipped with new, high-tech weapons and armor.
- Fought in by the United States 135 to 132 years preceding the cumulative Great War, the World War II saw the extensive utilization of all branches of the United States Armed Forces onwards from the 8th of December, 1941 with the US Declaration of War against Japan, and successively, numerous other Axis nations and its aftermath witnessed the gradual establishment of an independent air force in 1947.
With the nuclear holocaust of 2077 and the dissolution of the chain of command, the U.S. Armed Forces effectively ceased to exist, becoming groups of isolated soldiers with no coordination. Two groups, the Enclave and the Brotherhood of Steel are known to be direct descendants (or include descendants of) the original United States Armed Forces. Furthermore, it is implied that the members of the United States' Armed Forces inevitably diffused into the general wastelander population, with some sections stratifying themselves based off perceived military heritage, such as the Desert Rangers of the Texas Commonwealth.
- Mariposa Military Base
- Lost Hills Security Bunker
- Sierra Army Depot
- Toxic Waste Dump Security Bunker
- Nellis Air Force base
- Hidden Valley
- Hopeville Missile Base
- Tibbets Military Prison
- Los Alamos
- MacArthur Army Base
- Bunker Alpha, Beta and Gamma (original names not known)
- Preoria facility
- Cheyenne Mountain
- Kansas City silo complex
- Fort Bannister
- Fort Constantine
- Fort Independence
- National Guard Depot
- Turtledove Detention Camp
- Wheaton Armory
- Rivet City Aircraft Carrier
- The Citadel (formerly the Pentagon)
- Albany Terrorist Prison, New York City