a place called Massingguard, which I’ve never yet managed to find on any map
Sounds like Mazingarbe in the Pas-de-Calais,
here.
From Wiki:
"The creation of a treatment plant and coal processing plant in 1896, which later became a large chemical complex, significantly enhanced the town......The
Second World War didn’t spare the town either. An
Allied aerial bombardment of the factories and mines, in September 1943, claimed 27 civilian victims."