German victories in Europe using mobile firepower made the development of light tanks a priority. In early 1942 the GMC Cadillac Division developed the M5 series tanks called the Stuart by the British. By September 1942 the improved M5A1 was developed. Originally equipped with a .30 caliber anti-aircraft machine gun most tank crews upgraded to the .50 caliber machine gun. In Europe the Stuart proved too ineffective against the larger German AFV’s making it an easy target. The M5A1 proved adequate in the Pacific against Japanese armor.