These are pictures of a British Mark 3 helmet.
After almost 30 years of using the famous brodie helmet it was time for helmet offering more side protection.
The new design was designated the Mark 3, it soon got his nickname turtle helmet.
Looking at the picture below, you understand immediately why:
I haven't found any date or manufacturers inscriptions in this helmet, probably hiding under the grainy paint.
That it is a Mark III, you can see by the location of the rivets that hold the chin strap lugs and by the screw
on top of the helmet holding the liner.
See my MKIV articles for comparison.
United Kingdom MKIV Black
United Kingdom MKIV Green