The Rochdale Observer on 31 October 1914 carried an advertisement for fireworks that read:
Ask for “Black Maria” or “Jack Johnson” shells
Wholesale House :- Edwards & Bryning Ltd, ...
and the Western Gazette 11 December 1914 carried an advertisement for a box of 100 toys marketed by the Allies Toy Co in Brighton, which included a scenario described thus:
Boom! – Oom! – Om! – M! – Bang!!!
The “Jack Johnson” great German Gun is at work. First 25 harmless shells explode with a bang, then the Red Cross Nurses and their white Tents appear on the scene to deal with the wounded.The term is used here for the gun rather than the shell, a late occurrence for this usage, but not an isolated incident.