Of course, you know by now that that is army. Here's war-time footage showing them in use. https://www.youtube.com/watch?v=l-jIrRwOzgM

The latter half shows Civil Defense in action in an air raid drill. You can see that all helmets were numbered, but this film gives you the understanding that those numbers were not for inventory, but rather to tell the "guy wearing helmet 51 not to stand in the way of the water hose, etc".