Part of logic behind the new tank's massive size is that soldiers inside a vehicle are more likely to survive an explosion if there's adequate space for them to wear armor while seated. The extra space also helps distribute pressure from the blast and thus lessens its impact. Another reason the GCV is so huge is that it's required to carry a larger gun than the Bradley does; the new tank will hold a 30mm cannon, probably the 344-pound Mk44 Bushmaster II. Finally, the GCV's extra weight means it will need to be manufactured from the start with a more powerful engine. (By contrast, the Bradley got heavier as the Army added armor to it in Iraq, and its original engine wasn't powerful enough to support the extra weight.)