The first rifle produced by Armalite began in 1952 as a project between the brothers-in-law, Charles Dorchester and George Sullivan (no relation to later Armalite engineer L. James Sullivan). Sullivan is the chief patent attorney for the Lockheed aircraft company, and the two have the idea to produce an ultra-light rifle using aircraft industry materials like fiberglass and aluminum. They create a company called SF Projects and get to work using Remington actions. They fit aluminum (and then later aluminum/steel composite) barrels and foam-filled stocks and the result is a rifle that weighs less than 6 pounds with a 4x scope fitted. The first ones are chambered in .257 Roberts, but this shortly gives way to the new .308 Winchester cartridge.

Sullivan and Dorchester make a connection with Richard Boutelle, who is very much a "gun guy" himself and also head of the Fairchild aircraft company. The idea of the rifle appeals to Boutelle, and Fairchild was looking to diversify its operations - and so Fairchild agrees to buy SF Projects, renaming it the Armalite Division of Fairchild.

The idea of the rifle was for civilian hunters who want a gun that is light to carry for long distances and also military specialists like airborne troops who need lightweight gear. The Army tests the AR-1 in 1955 and finds some fairly serious problems with it. There are reliability issues, and also accuracy shortfalls. When the composite barrel heats up, differential stresses cause the point of impact to shift. This foreshadows the catastrophic failure of a composite barrel in AR-10 testing, but that is a story for another video. Ultimately after two rounds of testing the Army rejects the rifle, and that is pretty much the end of it. Armalite moves its focus to other projects, namely combining aircraft industry materials with the self-loading rifle of their other designer, Eugene Stoner. That, of course, will become the AR-10.

Since I know folks will ask, the AR projects between 1 and 10 were thus:
AR3: Stoner-type rifle in hunting configuration
AR5: Air Force survival rifle
AR9: Shotgun
The designations 2, 4, 6, 7, and 8 were set aside to drawing board projects that never materialized.

Thanks to the Springfield Armory National Historic Site for giving me access to these rare specimens from their reference collection to film for you! Don't miss the chance to visit the museum there if you have a day free in Springfield, Massachusetts:
https://www.nps.gov/spar/index.htm