I am sure these have been covered here before, but I thought I would share my much loved example.
A 1955 Dutch MkII clone, a Verernigde Blikfabrieken (United Tin Factories) made Civil Defense helmet. This model was made before this date and they were issued to the Army, however in 1956 all were destined for the Civil Defense dept. It is my understanding these attractive helmets were in use until the 1980's.
Not sure the origin of the net, it's too small to be an American M1 net, perhaps Commonwealth?