The other thing about these depots that not many people know about, is that apart from filling shells and aircraft bombs there were also things called "Bulk Contamination Vehicles" These were a cross between a petrol tanker and a farm slurry sprayer. If the Germans had invaded the BCVs would have been driven along roads that the enemy had to cross, with the pumps running and laid a 30 odd yard wide belt of Mustard gas in front of the advancing Germans, to cause casualties and slow them down. It's probably just as well the Germans never did invade, as faced with belts of contaminated land in front of their troops they may well have responded with Tabun, Soman and Sarin the first of the nerve agents that we knew nothing about at the time and had no protection against.
(Black Shuck I hope you don't mind me posting this, I'm not trying to steal your thunder but I thought that people might be interested) Gordon