This Beleta chronograph was issued by the Belgian airforce in the 40s. It features a cool dial with a telemeter and a snail type tachy.
The markings on the case back stand for 'Aviation Militaire Belge' which was the name of the air arm before the airforce was founded in 1946.
6B234 is the British marking for a pilot's watch which makes sense because Belgian pilots served in the RAF during WW2 and the airforce was created to the example of the Royal Air force.