Just for comparison here is what I believe is referred to as the "USAAF Protective Flight Helmet Style" or P1 helmet. I believe this was a manufactured jet helmet rather than a modified item. This was worn over a cloth or leather flight helmet.
hello, thanx for posting this very interesting picture in large size and full of details.
Just a note on my part, this one should actually be the so-called Style 1 helmet, put over a standard soft flight helmet, not a P-1. The P-1 is a true one-piece, hard constructed helmet and much likely could be the new, official name of the Style B-1, this in turn being derived from the Style B helmet.
The Style B had a prominently flattened crown, very much like the famous 'Dr. Lombard's Helmet' that eventually gave birth to the 'Toptex 3 BM' model.
'Style B-1's nomenclature, but virtually with no changes at all in the item itself, might have been changed into the 'P-1', I believe around November (or, maybe October?) 1947. Sure the P-1 was since the beginning a 100% operational model, and the 'Style B-1' much likely as well; possibly not so for the 'Style B' helmet (even though almost identical to B-1).
In my opinion many a helmet we can see in photos from 1948 up to early 1949 when only P-1 helmet are mentioned being worn by operational units, might be actually 'Style B-1' specimens still in use by then.