Army Field Manual (FM) 3-99, Airborne and Air Assault Operations, establishes doctrine to govern the activities and performance of Army forces in forcible entry (specifically airborne and air assault operations) and provides the doctrinal basis for vertical envelopment and follow-on operations. This publication provides leaders with descriptive guidance on how Army forces conduct vertical envelopment within the simultaneous combination of offense, defense, and stability. These doctrinal principles are intended to be used as a guide and are not to be considered prescriptive. FM 3-99 encompasses tactics for Army airborne and air assault operations and describes how commanders plan, prepare, and conduct airborne and air assault operations by means of joint combined arms operations.