Gun depression
How far below horizontal a gun can point, which decides whether a vehicle can shoot over a crest without exposing its hull.
Also known as depression, gun dep.
Depression is measured in degrees below level. Ten degrees is generous, five is restrictive, and the difference decides which ridge lines a vehicle can use.
It is what makes hull down positions possible. A vehicle with strong depression parks behind a rise, drops its gun over the top and presents only a turret, while a vehicle with poor depression has to crest the ridge and show its hull to take the same shot.
Depression usually varies around the turret: many vehicles lose several degrees when the gun points over the rear or across the tracks, which is why a good position accounts for which way the hull is facing.