Armor with two or more plates spaced a distance apart falls under the category of spaced armour. Spaced armour can be sloped or unsloped. When sloped, it reduces the penetrating power of bullets and solid shot, as after penetrating each plate projectiles tend to tumble, deflect, deform, or disintegrate; spaced armor that is not sloped is generally designed to provide protection from explosive projectiles, which detonate before reaching the primary armor. Spaced armour is used on armoured military vehicles such as tanks and combat bulldozers. In a less common application, it is used in some spacecraft that use Whipple shields.