Kirk Butler, right, director of operations for the Hypersonic Systems Test Branch of Arnold Engineering Development Complex, explains how the Aerodynamic and Propulsion Test Unit operates to Maj. Gen. Evan Dertien, commander, Air Force Test Center, during Dertien's visit to Arnold Air Force Base, headquarters of AEDC, Oct. 13, 2021. The Hypersonic Systems Test Branch of AEDC provides a unique, vertically-integrated capabilities set to support the hypersonic testing needs of the Department of Defense. The Branch is involved in every step of the developmental process for test and evaluation of hypersonic systems. (U.S. Air Force photo by Jill Pickett)