DEVICE FOR ACHIEVING AIM-OFF FOR A FIREARM

A gun is described in which a gun barrel and a gun sight are mounted for movement together in deploying the gun in azimuth and in elevation under the action of servo drive means. A tracking unit is provided to control the servo drive means, which may comprise separate servo motors for rotating an upper mounting of the gun in azimuth and for rotating the gun barrel in elevation relative to the upper mounting. The tracking unit has two separate phases of operation. In its first phase of operation, the tracking unit produces controlling signals which represent the behaviour of a target as sensed by a gun layer controlling an aiming device and a rangefinder to produce aiming and range signals which form inputs to the tracking unit. In its second phase of operation, the tracking unit produces controlling signals which represent a predicted behaviour of the target by maintaining constant a function of the controlling signals which is determined by the particular nature the controlling signals take and the assumed behaviour of the target. When the controlling signals represent the Cartesian coordinates of the position vector of the target, and it is assumed that the target is moving with constant velocity along a straight line at the time of firing the gun, the time derivative of the controlling signals is maintained constant. Auxilliary circuits are described by which aim-off corrections may be made on the basis of the estimated time of flight of a projectile to the target depending on known ballistic properties of the projectile and on ambient atmospheric conditions.