Cortébert Air Ministry 6B/159?

Hi all, I'm aware that Cortébert produced ATP watches - but I've just encountered this example online and was intruiged. I've only found one other example online and i believe it to be the same piece.

I'm looking for an appropriate watch for use mainly within a WW2 living history setting (RAF ground crew, in honour of my great grandfather).

Does anyone know if this has any grounding or is completely unfounded - as it seems a reasonable price despite the worn case (which isn't necessarily an issue for what I'm using it for) if so?

I'm new to vintage watches but didn't believe them to be on the list of manufacturer for Air Ministry watches for WW2...

Thanks for you knowledge.

2 mistakes in the engraving: the I in I59 is just a straight stroke . No hook. Other parts of Europe have that hooked One. And : the 6B here has no closed 6, but seems open. Whoever did this, what not in England in the 1940's.

As I suspected, but wished externally reproduced. Many thanks!