In the above photograph of a typical Mk IX Sextants transit case, the letters indicate as follows:-
A. Is the base of the spare lamp tin. 2 Lamps are usually wrapped in tissue paper or cotton wool.
B. Is a black composition block with two holes into which the power plug fits.
C. Is an unusual composition cover for the spare lamp tin. I have seen several of these and they are all the same so either they were produced to a drawing in station workshops or, more likely made to fill a production gap at the makers.
D. Normal tin lid for spare lamp tin. Spare lamp in each lid
E. One of the two spare battery tubes (With batteries)
F. The other tube in a stowage position.
G. Eliminator mounting. The mountings location varies from Vertical, as this one, or Horizontal across the top of the case.
H. Battery eliminator. Used, not as I originally thought, in case all six batteries were low, but to give a suitable voltage at the low temperatures experienced at altitude. I tested some typical modern cells at minus 20°C and found they only supplied about 1Volt, well down on the 1.5 Volts the lamps were designed for.
All transit cases contained the above items under normal conditions. The actual clip positions vary between models and the padding can vary. Usually the pads are suade leather held in place with black Bostic adhesive, felt is also used a lot. I have seen cases lined with foam rubber, this usually has started to deteriorate and can make a nasty mess of the instrument. The only solution to such a problem is to remove the foam and clean it off the sextant. Early models of the Mk IX left the makers in an aluminium case. This was soon stopped once wartime restrictions came into place as aluminium was a strategic resource. The fiber material was then adopted for all the later versions and you will note it is treated as wood with brass nails holding the case together.