Originally Posted by
wondering
From Wikipedia:
The BMP-1 and BMP-2 series vehicles share a major drawback with many Soviet tanks. Ammunition is stored near or even inside the fighting compartment, which makes them more vulnerable to a hit from an anti-tank round or a missile across the side arc. If that happens, the ammunition often explodes, killing everyone and completely destroying the vehicle.[43] During the fighting in Afghanistan and Chechnya, hits by RPGs penetrated the BMP-1's armor in 95% of cases. This often resulted in the vehicle burning until the ammunition exploded.[42] Due to these limitations, Soviet/Russian soldiers customarily rode on the outside of the BMP-1, sitting on top of the hull while in combat zones.[46]
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As did the Americans in Vietnam, who would often ride on top of the M113 sitting on flak jackets, because of their worries about hitting a mine, as the APC was built out of aluminium.