A line of rucksacks and dummy M4s are positioned for Airmen to use during the rucksack march portion of the security forces defender competition on Joint Base Andrews, Md., July 23, 2018. The defenders competed to represent the Air Force District of Washington in the Defender Challenge 2018 at Camp Bullis, San Antonio, Texas. The challenge will focus on the capability, lethality and readiness of each team. (U.S. Air Force photo by Airman 1st Class Michael S. Murphy