An interesting item, not often seen in the UK, but this is an American Civil Defence helmet, based on the British Brodie helmet design (also used by the Americans pre M-1 helmet). Essentially, the American A.R.P. and although they never saw an air raid, they were similarly well organised as the British wardens.
This was is complete with liner and has the blue circle, with red and white striped triangle, denoting use by an Air Raid Warden.
No maker mark found but split pins holding the bales in place, so this is American manufacture, not British and re-used. Liner is a little tatty, with the tar paper deteriorating. Original strap is present though.