Age of Darkness is a mod set in the historical period spanning the two world wars of the 20th century, revolving around the struggle between the forces of liberty, socialism and reaction.
US forces in Age of Darkness are depicted as being militarily awkward at the start, but over time can obtain a research capability for tanks that is on par with that of the Soviets - so while you may struggle to otain the M1 or M2, obtaining Chaffees and Shermans is a breeze but only as long as you can survive till the Mechanisation Era. So smaller factions like Japan and Italy have a window of opportunity to beat the Americans - in the early game, that is. Fortunately, the Americans retain the same vanilla bonuses, so getting enough scientists and resources isn't too much of a trial as long as you can play defensively in the first half of any game.
Although it received an armour upgrade and a new turret configuration, the M2 "Medium" was still somewhat lagging behind most contemporary European armour designs. In Age of Darkness, the M2 is represented by both "Mae West" and "Medium" models, and while rather costly to research, is a vital step in obtaining better tanks.