Actually, the T12 was not created as either a tank destroyer - a term which came into existence after its development - or training vehicle. It was the initial attempt to develop a self-propelled mount (SPM) for the field artillery of the armored division. It was simply available at Aberdeen in June-July 1941 when the initial tests of the new antitank doctrine was tested at Fort Meade. In December, when the Tank Destroyers were created it was chosen as the interim self-propelled mount for the ten "heavy" battalions organized. By that time the field artillery had passed on it because they wanted a 105mm SP, given that the 105mm was selected to replace the 75mm as the divisional DS piece. The T19 then was tried, but of course even more overloaded the half-track chassis so was quickly discarded. The T12 and T19 combination then was tried as the interim weapon for the Infantry Regiment Cannon Company where they did reasonably good service, but foundered on McNair's dislike of SP artillery and "excess" divisional combat vehicles.