FM 21-5 Military Training . By United States. Department of the Army

"The mission of the Army, as a part of the Armed Forces of the United States, is to provide for the security of the United States and for the support of its national and international policies. To accomplish this mission, the Army must be ready at all times to undertake land combat operations and sustain them indefinitely. The traditional policy of the United States is to maintain an Army of minimum size consistent with the immediate needs of the nation, but one that is capable of rapid expansion in the event of a national emergency. This policy demands the ability to mobilize rapidly. Because time is all-important during mobilization, training requirements during that period must be reduced to essentials. Peacetime training must serve to determine which requirements are essential and must provide a force ready for immediate combat in the event of a sudden attack