U.S. Marine Corps Lance Cpl. Zachary Cooper, a radio operator with 3rd Amphibian Assault Battalion, 1st Marine Division, uses the AN/PRC-117 Multiband Manpack Radio to set up communication during exercise Steel Knight at Marine Corps Air Ground Combat Center Twentynine Palms, California, Dec. 5, 2019. SK20 is an annual training exercise executed by approximately 13,000 Marines and Sailors designed to improve and assess the 1st Marine Division's ability to fight and win against a peer or near-peer threat.