Land Mines,

An Amtrac's worst enemy is a heavy anti-tank mine which can split the hull of an LVT and cause the fuel bladders to rupture and burn. For this reason, the Marines of the 1st AmTrac Battalion sandbagged the floorboards of their LVTs and infantry personnel rode on top of the AmTrac. While this practice prevented some injuries from exploding landmines, it didn't prevent all injuries and it left infantry personnel exposed to the other dangers of a combat zone.