Massif Army combat shirt Large The Massif Army Combat Shirt (ACS) is the standard for hot-weather combat gear. A progressive design incorporates feedback from thousands of soldiers in some of the world's most unforgiving environments. Our innovative FR fabrics are lightweight, breathable, and highly wicking. With four-way stretch, a performance fit, and uncompromising FR construction, the ACS is engineered for FR protection and exceptional comfort under armor. Over five million shirts fielded by the U.S. Army.