It saw a lot of duty.
SAT: The History of the Army's M4 Carbine and the Wars It Went To
In the early 1990s, the Army purchased a limited number of M4 carbines. The M4 had a collapsible stock and a shorter, 14.5-inch barrel, as opposed to the longer twenty-inch barrel of the M16A2. That made the weapon easier to carry in tight spaces, particularly armored vehicles and helicopters, while also easier to operate on close-quarter battlefields such as cities or jungle.
The U.S. Army is an armed force with a truly global reach. At any given time, America’s premier land power operates on several different continents simultaneously, from hot, dry deserts to humid jungles and sprawling cities. Its infantrymen carry a weapon whose lineage dates back to Vietnam but which has been constantly improved to become the weapon it is today. Rugged, simple and accurate, the M4 carbine is the standard infantry weapon of not just the Army but all of America’s ground forces.
(This first appeared several years ago.)
The story of the M4 goes back to the mid-sixties and the early days of the Vietnam War. The Pentagon, mulling sending hundreds of thousands of troops to South Vietnam, wanted a small, lightweight service rifle to replace the larger standard-issue M14. The new AR15, or Armalite Rifle-15, was smaller, lighter and fired a smaller 5.56-millimeter bullet. A soldier carrying the AR15, later designed the M16, could carry twice as much ammunition as a soldier carrying the M14. Demographic trends also meant that more and more soldiers were coming from cities and unfamiliar with firearms, and the M16 with less recoil was easier to train soldiers to proficiency.