Direct proof of use
The clearest public record for 5.56x45mm NATO-family ammunition in the 2001 War in Afghanistan is the U.S. Army's June 23, 2010 announcement that it had begun shipping the M855A1 Enhanced Performance Round, a new 5.56 mm cartridge, to support warfighters in Afghanistan. The same announcement said soldiers in Afghanistan would begin using the new round that summer.
A later U.S. Army article on the M855A1 program ties the replacement effort to combat feedback from Iraq and Afghanistan. It states that field reports and post-combat surveys from those theaters discussed the existing M855 round's battlefield performance, while describing M855A1 as the Army's improved 5.56 mm general-purpose round.
Sources: Army begins shipping improved 5.56mm cartridge, Evolution of the M855A1 Enhanced Performance Round
Timeline
The Army adopted the M855 5.56 mm round in 1982 after earlier M193 service, linking the cartridge family to the M249 Squad Automatic Weapon and the M16A2 rifle. During the Afghanistan war, the documented public transition point was June 2010, when the Army announced M855A1 shipments for Afghanistan and planned large-scale follow-on production.
By November 2010, the Army's acquisition community was describing the M855A1 program as a response to performance consistency and environmental concerns, citing Iraq and Afghanistan combat feedback as part of the background for replacing the leaded M855 service round.
Sources: Army begins shipping improved 5.56mm cartridge, Evolution of the M855A1 Enhanced Performance Round
Role in the conflict
In Afghanistan, the cartridge's documented role was infantry small-arms ammunition for U.S. Army weapons rather than a separate platform or munition with independent tactical employment. The Army described M855A1 as tailored for the M4 weapon system and as improving performance in the M16 and M249 weapon families, which placed the round within the standard rifle, carbine, and light-machine-gun ammunition chain used by soldiers.
The available direct sources support shipment, fielding, and expected soldier use of M855A1 in Afghanistan, plus Afghanistan-linked field feedback on the earlier M855. They do not identify a specific firefight, unit action, or individual ammunition lot in Afghanistan, so this page treats the record as theater fielding and small-arms ammunition use rather than an incident-by-incident combat history.
Sources: Army begins shipping improved 5.56mm cartridge, Evolution of the M855A1 Enhanced Performance Round