First developed during the Korean War, the Mitchell pattern camouflage was first used by US Marines with their shelter halves in 1953. The helmet cover soon followed in 1959 and was used for the M1 helmet by both Marines and Soldiers during the Vietnam War. 
These were reversible with the first side being practical for the jungle and the second side practical for the desert. The covers had slits in them so that foilage could be added to improve the camouflage of the helmet. 
 
These are all dated DSA (Defence Supply Agency) 1973. 
 
Originals are becoming harder to find so make sure to grab one before they are gone!
 
As these are original, please expect your cover to have fading, small tears, and/or fading. Otherwise, they are ready to go. 
 
There is one grade 2 cover that has significant tears and fading but can still be placed on your M1 helmet.