the military use depleted uranium in , among other things , their armour-piercing rounds in tank and aircraft ammunition , and of course mere civilians can not get that material for that purpose , they can use it as trim weights in aircraft ( it is extremely heavy for its size ) and a few other mundane things but definitely not in weapons , so as the fourth light came on it automatically sent a signal to the pneumatic discharger to send a projectile up the tube ( which had been secured between the floor and a specific point on the ceiling ) and it penetrated the polystyrene ceiling tiles and a smidging of plaster .