The mission of the HQ 138th Regiment (CA) INRTI is to provide regionalized combat arms individual training, including military occupational specialty qualification (MOSQ), additional skill identifier (ASI), and noncommissioned officer education system (NCOES) training for the Army National Guard, the United States Army Reserve (USAR), and the active component (AC).

The 138th Regiment provides management and quality assurance oversight for the functionally aligned 11B TASS battalions within region D and monitors and coordinates academic instruction, for soldiers participating in courses at its training sites that include MNRTI and WIRTI. The 138th Regiment works in conjunction with the National Guard Bureau (NGB), the TRADOC Coordinating Element the regional coordinating element, and the TRADOC Combat Arms proponent school at Fort Benning GA. The 138th Regiment plans and programs training within its region based on requirements identified by the state, individual training branch (NGB-ARO-TI), the Army Program for Individual Training (ARPRINT), and the Training Requirements Arbitration Plan (TRAP).

The Indiana Military Academy was established in February 1956. It was the fifth such school to be established in the United States. There are now fifty-two such schools in operation throughout the nation. The process and high standards of the Indiana Military Academy were noted in military circles on local and national levels. This recognition resulted in bringing a national conference, sponsored by the National Guard Bureau and attended by delegates from all the states, plus Alaska, Hawaii, and Puerto Rico, to Indianapolis in January 1957. Many of the operational techniques employed by the Indiana Military Academy have been recommended by the National Guard Bureau for adoption by similar type schools in the United States.

Today, the Indiana Military Academy not only provides training for Officer Candidates, but provides combat arms training for all levels of enlisted and non-commissioned officers. The academy is also the primary source for Military Occupational Skills (MOS) qualifications for combat support, combat service support, and combat MOS's for active, ARNG, USAR and is part of the Total Army School System.