Hi Roger,
oh to have a "boffin" in my family, sigh...

Re the railway, as the frontlines in WW1 were extensively served by railways albeit narrow gauge I think, does that mean they were worked by conscripts who were presumably ex-Railway men, perhaps those of a younger age than your ancestors ?.
I know both sides extensively used tunnelling companies to undermine the trenches, but I gather it was only the allies who deliberately employed those who were already miners by trade in these companies, perhaps because the British coalfields then were larger so had a greater speciallised workforce than their enemies ?.

In WW2 my dad was very lucky that due to being an asthmatic child he didnt follow his father/forefathers down the Lydbrook pit, so when war brokeout he was a young lad with the local bus company and became a RO with them, taking many hundreds of Foresters day & night to the aircraft factories nr Gloster etc.