Originally a nautical
term for a ship whose superstructure
was visible, but whose hull was still below the horizon line
, the term "hull down" is now commonly used to describe one of the most basic tactics in armoured warfare
. This involves bringing a tank
up to a ridge, wall or other form of cover
, so that the turret
is visible, but the hull
is still covered. In this position, the tank's weapons can be used freely, but the largest part of the tank remains protected. This is the ideal defensive situation for a tank to be in, and a platoon
of tanks in a good hull down position can hold off numerous attackers, often surviving until they run out of ammunition or are forced to leave their positions. The extensive use of hull down positioning is one of the reasons the Israeli Merkava
was designed with a very small turret.
Even though most of the tank is covered, a tank should never remain stationary after hostilities have commenced. Forty seconds is the longest you want to stay in the same position - after this it is almost inevitable that you will be targetted and destroyed. Even forty seconds is longer than most tank commanders like to stay hull down. Typically a tank will fire one or two series (a series is a maximum of four rounds or two hits), reverse quickly while activating a smokescreen, do a reverse S-turn to a new position along the ridge, and pull up slowly to a new hull down position. This is most effectively performed by a platoon of three or four tanks (Israeli platoons have three tanks each, but most Western forces use platoons of four) spread out along a long ridge.
Although I have used the word "ridge" here, many natural ridges are not good for hull down positioning, because the angle of the ground makes it difficult to depress the main gun far enough to effectively cover the near ground. The tank really needs to be almost horizontal to be effective. Most armies try to prepare the ground they are planning to defend by digging flat hull down positions ahead of time.
NOTE - please don't forget to lower your antennas when approaching a hull down position, unless you really like being destroyed the instant your turret is exposed.