This United States Marine Corps USMC manual, Marine Corps Reference Publication MCRP 3-10F.2 Supporting Arms Observer, Spotter, and Controller February 2021, provides the techniques and procedures for requesting, adjusting, and controlling mortars, artillery, naval gunfire, and close air support. Changes in technology, equipment, organization, and methodologies have necessitated the update of this publication. It is intended as a field reference for supporting arms observers, including mortar and artillery forward observers, naval gunfire spotters, and forward air controllers. Additionally, it serves as a study guide and field reference for personnel seeking information on supporting arms procedures.