Hey Ron,
It is British, but named to two Canadina officers.
Captions for your photos
#1 US troops with SBR
#2 British troops with SBR
#3 PH hood in a private collection in Australia
#4 French M2, the mask on the dog is not a special mask for a dog, the soldier is holding it on for a photo
#5 This horse mask is much later than WWI
Best
gus