A need exists and has existed for a substantial period of time for an adequate magnetic heading reference system, i.e., "compass," for use in military vehicles, such as tanks. It is believed that this need was first recognized during World War II as evidenced by a War Department Equipment Board Report dated Janurary 1946.
To provide an adequate compass system for a tank poses special problems due to the extremely high "magnetic signature" of the tank. The magnetic signature may be defined as the aggregate error generated by the total magnetized material in the tank, and the magnitude of the error varies with the relationship of the turret to the body of the tank. If one attempted to use a float-type, self-contained compass (the so-called "wet" compass) in a tank, the magnetic signature of the tank body would cause the compass to produce erroneous heading readings. Further, it is believed that, with a wet compass, it would be virtually impossible to adequately provide compensation for the magnetic signature.
Compass systems for tanks have been proposed which involve obtaining heading information from outside the zone of influence of the magnetic signature and transmitting the heading information to an indicator in the tank. One such system includes a transmitter, which is mounted at the top of a mast, which is connected to the body of the tank. While this technique operates to reduce the effects of the magnetic signature of the tank, it creates other problems. For example, the mast can interfere with firing, especially when located on the front of the tank. Also, the mast is susceptible to being damaged or destroyed through rotation of the turret of the tank with the gun in a lowered position. Moreover, the height of the mast could significantly alter the silhouette of the tank, thereby making it more readily identifiable by the enemy. Thus, this approach has not solved the long-standing problem.
Quite apart from the problem of compensating for the magnetic signature of the tank, a "wet" compass is prone to produce heading errors above and below the seventieth parallels. These type errors are due to the declination of the earth's flux lines as they converge on the magnetic poles.
Tanks typically utilize information received from spotter planes and forward observers to position the gun of the tank to engage targets. Once the tank has fired a round at the target, it is often the case that its location will be observed by enemy spotter planes or enemy forward observers. It is, therefore, advantageous, if not absolutely necessary, for the tank to change its location after firing a round. In order for the tank to be able to engage the same target from its new location, the gun must be repositioned at that new location.
No gun control system for a tank has heretofore been available which continuously maintains the gun aimed in the direction of a given target, regardless of the direction of travel of the tank. The foregoing deficiencies and shortcomings of the prior art have been overcome by the present invention.