As a preview to the main discussion, the role of the Twin Gyro Unit as a component part of the weapon's guidance system is first described. The reader will appreciate that there are as many types and configurations of gyro units as there are weapons and a full treatment of the subject would be beyond the scope of this paper. For the purposes of the discussion that follows, the gyro unit chosen is the two degree of freedom, electrically driven, Rotoraced displacement gyro, as used on the Sea Eagle, Anti Ship sea skimming missile.