A compass designed at the Royal Aircraft Factory, Farnborough, in 1915 and known as RAF Mark II.

This Mark II was the result of the experiments of Keith Lucas at Farnborough. The compass bowl is spherical, the verge glass being concave on its inner surface, and has an expanding diaphragm. The inside of the bowl is painted white with a black lubber line . A small window on the front allows an observer to note the course steered.

The card is a mica ring, graduated on the inner surface to every 10° in white on a black background. It is mounted on a flat float, in which the two needles are accommodated, and is fitted with an inverted pivot. The float is painted red and blue according, as was standard at this time, and an arm projecting from the side of the bowl engages in a recess in the float to prevent it from coming off the pivot.

The four metal strips, which connect the card to the float, are arranged so as to form damping vanes. These cards balanced so as to remain horizontal in England and France but, with the centre of gravity high, they would be liable to lose their balance if used in latitudes where there was any material alteration of the Earth’s vertical force.

The bowl is mounted in a square container, to the bottom of which a magnet carrier is secured. The anti-vibrational arrangements consist of a “floating plate” with two slots working on pins in one lateral direction only. The bowl is capable of working by means of two pins engaging in slots on the plate in a direction at right angles to the former movement. Four leaf springs are fitted on the bowl to control its movements in the container and, when well made, this suspension gave good results under vibration. Unfortunately many of these compasses were made by engineering firms without previous experience in compass making and the results were not uniformly satisfactory; the output was low, due partly to the inexperience of these firms and partly to the fact that this type did not appear to lend itself to rapid production.

In this specific example the card was fitted to its frame and needles so as to record True courses in France (see also ACO.276).