Machine-gun Bunker is a extremely effective defensive structure that excels at stopping infantry assaults. suppresses enemy infantry, slowing down their movements while ripping them to shreds. However, AT guns and tanks have an easy time destroying them.
Anti-tank Bunker is the tank version of the machine gun bunker. It deals heavy damage to tanks and other vehicles, however, differing from the machine gun bunker, is the ability to be upgraded with the anti tank guns and armor piercing shells, allowing them scale better into the late-game as terrors to enemy tank masses. However, they do not possess the ability to attack infantry, so approach them with flamethrowers for quickly shred them if machine gun bunkers are not conjoined with them.
There is an additional variant which is just a bunker that can load troops inside. Both bunkers can be upgraded to become even stronger at the Tech center.