Military Slide Rules & Calculators

Graphical Firing Table M13

I have no information available on this World War 1, World War 2? gunnery slide rule. It is in excellent condition and has two additional slides in the case.
The scales are painted on wood.
The rule is approx: 18 x 3inches (46 x 7.5cm) in a fitted leather case. There are also C and D scales for multiplication/division.
There is a small thumb-wheel half way along the bottom of the stock to enable the slide to be locked in position (Shown on scan of backplate tables).

Firing Table M13