sloped armour provides increased protection for armoured fighting vehicles through two primary mechanisms. the most important is based on the fact that to attain a certain protection level a certain volume has to be enclosed by a certain mass of armour and that sloping may reduce the surface to volume ratio and thus allow for either a lesser relative mass for a given volume or more protection for a given weight. if attack were equally likely from all directions, the ideal form would be a sphere; because horizontal attack is in fact to be expected the ideal becomes an oblate spheroid. angling flat plates or curving cast armour allows designers to approach these ideals. for practical reasons this mechanism is most often applied on the front of the vehicle, where there is sufficient room to slope and much of the armour is concentrated, on the assumption that unidirectional frontal attack is most likely. a simple wedge, such as can be seen in the hull design of the m1 abrams, is already a good approximation that is often applied.