So it's a rear seam stainless steel rim with no heat stamp that is painted blue? Sounds like a Belgian Airforce Helmet if it wasn't for the chinstraps.
I'm heading down the same path of thinking as Nitram is heading, assuming there is no sign of a heat stamp, unless of course it is just covered in paint however, from the photos provided, the interior paint does not appear to be too heavy and therefore a trace of the heat stamp should be seen of it does exist. The pictures are also not clear enough to see the dome profile to make a determination of it is high dome or low down. And although there was a very short period of time (about one month) US M1's were made with rear seam, stainless rims, this is a very common configuration with several of the Euro clones. The paint color is throwing me off a bit too, although it could just be the photos, but it looks as though the inside and outside colors are not of what would be typical for a US Navy helmet, although no real standard exists. Without better photos and a confirmation of a heat stamp, I'm of the opinion that the shell is a Euro clone with a fresh US or repro T-1 chin strap attached but better photos could prove this otherwise.
if the sun ever comes out again, I'll take some pics of it in natural light. I looked under a bright light with my magnifying glass and still don't see any markings, just where the paint had run.
47th MP Co/47th Inf Div 1983-1988
583rd Ord Co 59th Ord Bde Muenster, W Germany
Looking for P37 ammo pouch with No4 bayo frog