It was designated the T28 and tested at the Aberdeen Proving Grounds .
The M15 design developed from the United States Army Coast Artillery Corps ' T1A2 Multiple Gun Motor Carriage ( MGMC ) project , which added a 37 - mm gun to an M2 Halftrack Car .
M15 was designated the T28 and tested at the Aberdeen Proving Grounds .
The M15 design developed from the United States Army Coast Artillery Corps ' T1A2 Multiple Gun Motor Carriage ( MGMC ) project , which added a 37 - mm gun to an M2 Halftrack Car .