Thank you very much! It does seem to be a Swiss M18 but I have no idea what variant of the M18 it is. It has a "K" inside of it which from what I've read is short for Carl Kyburz, the producer of the helmet but otherwise doesn't appear to have any more markings of any sort.Swiss m18 of some variety, may have to check it for markings. See this thread: http://www.treasurenet.com/forums/what/273265-military-helmet.html