Hey, number 000_0156 is my old helmet...
We used those in the Norwegian Army until a few years ago.
The good old "Steel Pot"..
It's an American Vietnam war helmet, and I belive it's called M1.
more info here:
http://www.thevietnam-database.co.uk/Usmc/Mhelmets.htm
Maybe worth around $100 (-), you are missing a couple of pieces from the inside of it.
Don't know about the other ones.