American Military History, Volume 1 by Richard W. Stewart

Calhoun was convinced that the American frontier ought to be protected by regulars rather than by the militia. Calling the militia into active service, he wrote Brig. Gen. Edmund P. Gaines, was "harassing to them and exhausting to the treasury. Protection is the first object, and the second is protection by the regular force." But providing a regular force capable of protecting the frontiers north, south, and west, as well as the seacoast, was another matter. In 1820 the Congress called upon the Secretary of War to report on a plan for the reduction of the Army to 6,000 men. Calhoun suggested that the reduction, if it had to come, could be effected by cutting the enlisted personnel of each company to half strength. In time of war the Army could be quickly expanded to a force of 19,000 officers and men. This was the start of the "expansible army" concept.

On March 2, 1821, Congress passed the Reduction Act that cut the enlisted strength of the Army by half (from 11,709 to 5,586) but cut the size of the officer corps by only a fifth (from 680 to 540). Thus, even though the Congress had cut the end strength of the Army overall, its limited reduction of the officer corps confirmed that the idea of an expansible army was beginning to achieve a measure of acceptance. Calhoun, although concerned with the drastic nature of the cuts, pronounced himself reasonably satisfied. The retention of a proportionally larger officer cadre would allow the Army to expand more rapidly upon the approach of war. This was a key milestone on the road to recognizing that the Regular Army and its officer corps was the first line of our nation's defense rather than relying totally upon the militia or hastily raised, equipped, and trained volunteer units.