Compass, Hand Bearing, Type O.6.A., Ref 6A/1248, with Original Case
Here is a WWII-era Hand Bearing Compass, Type O.6.A., in its original wooden case, as used in aircraft of the British RAF Coastal Command.
The 06.A. is hand-held compass, used by an observer (hence the "O" designation. Reference numbers for pilot compasses began with "P") to take navigational bearings in situations where a fixed compass could not be used, or to determine correction factors for fixed compasses. The handle holds batteries (not included) to power an internal lamp, which would internally illuminate the bowl of the compass. With the bearing target sighted through the "V" atop the glass prism, the observer would read the direction of the bearing through the prism mirror as it is reflected up from the compass card. The markings on the compass card are reversed so that they appear correctly in the prism mirror.
This example is from the personal collection of RAF Wing Commander William James Hunter via his son, Dr. Allan Hunter. Wg. Cdr. Hunter (see photo) was trained as an RAF Observer, and responsible as a bomb-aimer, navigator, gunner, and radio operator. Wg. Cdr. Hunter and the crew of their Bristol Beaufort bomber were shot into the sea during an attack on the German battlecruiser Scharnhorst in July 1941, and was a POW for the duration of the war. His exploits can be read in his autobiographical account From Coastal Command to Captivity.
The compass measures ~4 inches diameter and ~9 inches long. The case is ~5x5 inches and ~11 inches tall. The compass fluid has evaporated but it is otherwise in very good condition for its age. The compass card rotates as it should. The mirror in the prism is slightly distorted, but the card can still be read through it. The small lamps is present but its operability is unknown. The rubber cushion inside of the case has deteriorated and softened.