A side note to American tank development was that an engineer, with the last name Christie, was an avid tank fanatic in the 1920s and 1930s. He developed a suspension that would allow tanks to traverse rougher terrain, go faster, and be more comfortable for the crew. THis is known as the Christie suspension.

The American army was not convinced of the tanks, let alone the Christie suspension. So Mr. Christie took his talents to Russia. He was quite instrumental in the development of the T-34 and its precursors. The Americans then used the Christie suspension in their models. For sure, the M4 models had that suspension.