This United States Army and United States Marine Corps manual, Army Techniques Publication ATP 3-90.99 MCTP 12-10D Desert Operations April 2021, is a dual-designated Army/Marine Corps manual that provides Soldiers/Marines with the concepts and techniques associated with conducting operations in a desert environment. The principal audience for ATP 3-90.99/MCTP 12-10D includes Army/Marine Corps commanders, leaders, staffs, and Soldiers/Marines. Trainers and educators throughout the Army/Marine Corps will also use this manual. ATP 3-90.99/MCTP 12-10D applies to the Active Army, the Army National Guard/Army National Guard of the United States, United States Army Reserve, United States Marine Corps, and the United States Marine Corps Reserve unless otherwise stated.