This is a French Helmet "Sous Casque radio char M51" Type 2.
Sous Casque means under helmet or liner. and could be used as a liner for the previous presented Model 51 TTA.
Radio Char means tank radio, this helmet was designed so it could be used together with a tank communication system.
This helmet is made by S.I.A Le Mans in 1955.
The N stamped next to the 55 tells us it is made of nylon.
The interior of this helmet is made just like the US M1 liner.
The text in the nape strap is "MADE IN FRANCE"