A gun stabilizer is a device intended to facilitate aiming a gun by compensating for the motion of the platform on which the gun is mounted. The primary armament of all US tanks was stabilized at least by 1944. Some attempt was made to stabilize Soviet tank guns as early as 1938. The Bradley Fighting Vehicle main gun is also stabilized. (The defensive guns of the B-29 bomber were also electronically aimed, though platform rotation was not the main problem for them.) This was an important factor in World War II, because it allowed much greater accuracy while moving and, in addition to allowing a faster average speed, the survivability of a vehicle in battle depends on its unpredictable motion.
The mechanism usually includes an angular reference device such as a mechanical or optical gyro and servo mechanisms. In the case of a tank, there is one servo stabilizing the turret and another for the elevation of the gun. The aiming is then done by control input to the mechanism, rather than directly on the gun. The control mechanism usually has other functions, such as applying super-elevation and leading the target according to its velocity, making it a fire-control system, and some guns are entirely automatic.