Abstract: A set of two two-degrees-of-freedom rate gyroscopes and three linear accelerometers are assembled in a single module adapted to be mounted within a single aircraft electronics control unit, the unit comprising a strapped-down attitude and heading reference system. The module base provides a common keyed support for the two pre-calibrated gyros and three accelerometers in intimate mechanical and thermal association. The two gyros are oriented in the base and the base oriented in the aircraft so that the spin axis of one gyro is oriented parallel to the aircraft Z axis and that of the other gyro parallel to the aircraft Y axis while the gyro pickoffs and torquers (input and output axes, respectively) are rotated or skewed forty-five degrees about the spin axes to positions such that the input and output axes lie along the slant heights of a forty-five degree half angle right circular cone, the axis of which lies along the aircraft X axis.