But not everyone who has used the M4 is so happy. Here's What You Need to Remember: The Army is working to correct the M4’s deficiencies. Earlier bullets were designed to penetrate Soviet body armor and sacrificed lethality for armor penetration. The new M855A1 Enhanced Performance Round, aside from being lead-free and “green,” yaws more quickly when passing through the human body, creating an internal cavity and causing massive damage. 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.