Military issued M1 Gas Mask. This is not the civilian issued MC1 gas Mask.  The military issued M1 design has the internal mouth cover to prevent your lenses from fogging during use. Issued to personnel Between 1960s to late 1995
 
The mask is made of a light greenish blue rubber
Light O.D metal for the lense rims.
6 Point elasticated head strap
Size S is Super Grade with filter
Size M is Unissued and still in packaging, as is the filter