The M3 AT Gun is a large, slow moving, slow firing, yet highly lethal Anti-tank gun that is moved by two crew members and is great for taking out groups of infantry directly or indirectly.
Before bazooka nerfing patch, they weren't quite as needed and were considered as a waste of TP in some cases. Since the nerf, though, they have became an extremely vital anti-tank units, being able to deal a considerable punch to any German vehicle that dares to enter the battlefield.
The shell's explosion radius is not as large as a tank shell's, but the damage is more concentrated so it is generally more effective as an Anti-tank weapon. The M3 AT Gun will cost 8 TP and comes with two replaceable operators.
The AT Gun is your version of the German PAK 38. Strategies often employ having more then one AT gun due to their fairly low fire rate. In previous patches it was common to have an 'AT stack' of AT guns in one trench. However, with patch 2.2.7b, this is no longer possible as the guns will not fire if they are too close together. This may discourage the use of the M3 to some players, as the guns are quite large and it's difficult not to stack them but still have an effective AT force made entirely of these.