U S ARMY AVIATION Challenge Coin with Velvet Presentation Box. This is a great looking US ARMY AVIATION challenge coin. Coin has reeded edges and is about 1 9/16" in diameter and is gold plated. Coin is contained in an acrylic air tight holder and displayed in an attractive black velvet presentation box which will make this a very impressive gift or presentation. An army aviation unit is an aviation-related unit of a nation's army, sometimes described as an air corps. These units are generally separate from a nation's dedicated air force, and usually comprise helicopters and light support fixed-wing. Prior to the establishment of separate national air forces, many armies had military aviation units, which as the importance of aviation increased, were spun off into independent services. As the separation between a nation's army and air force led to a divergence of priorities, many armies sought to re-established their own aviation branches to best serve their own organic tactical needs.