Precise navigation upon the ice-cap depends largely upon the accurate steering of a chosen course. This operation can be rendered difficult by three major problems commonly faced by Arctic and Antarctic expeditions. First, the absence of topographic features as points of reference; secondly, the loss of precision of the magnetic compass inside a moving vehicle and in areas adjacent to the Magnetic Pole; thirdly, the dependence of the astro-compass and similar instruments upon an unobscured Sun.

A simple method by which these difficulties are overcome was tested and found satisfactory during an inland traverse from Wilkes Station in November–December 1960 into an area not previously explored by land. The principle of this method is the use of a periscope-like arrangement of mirrors combined with a suitable sighting system to enable the driver to use his track astern to steer a straight course ahead.

The original device was installed upon a vehicle (a ‘Weasel’), already fitted with an astro-compass and a magnetic compass in order to function as the navigation vehicle of the train. The rear vision mirror taken from a ‘Traxcavator’ was used as the main ‘Track mirror’. It was pivoted at its centre point through the shorter axis. The mirror was mounted on a frame of two half-inch steel pipes bolted on to the vertical wall of the well between the windscreen and the forward hatch of the Weasel.