 The 75 mm gun had a white phosphorus shell originally intended for use as an artillery marker to help with targeting.M4 tank crews discovered that the shell could also be used against the Tiger and Panther—when the burning white phosphorus adhered to the German tanks, their excellent optics would be blinded and the acrid smoke would get sucked inside the vehicle, making it difficult or impossible for the crew to breathe.This, and the fear of fire starting or spreading inside the tank, would sometimes cause the crew to abandon the tank.