Whilst many hand-held infantry anti-tank weapons will not penetrate the front armor of a tank, they may penetrate the less heavily armored top, rear, and sides. Anti-tank weapons can damage the tracks or running gear to inflict a mobility kill. Early WWII tanks had open vision slits that could be fired through to kill the crew. Later tanks' slits had thick glass, as well as sights and periscopes which could still be damaged with powerful small arms such as anti-tank rifles and heavy machine guns, hampering the crew. If all else fails, the hatch could also be forced open and grenades thrown inside, although later tank designs often have hatches designed to be difficult to open from the outside.