When the USA enter WWI, in 1917, their army still has no helmet. The troopers will therefore use the English Birmingham pattern with some variations. Our reproduction is a copy of the 1917 one, which what quite ingenious : small parts of rubber pipes are used to make the helmet adjustable, a rivet on the top fix the padding, and so on.
On sized, 58-63 head perimeter. Diameter 30cm.