Unknown US Navy helmet

Message 911:
I am just full of news today. I have enclosed a couple of photos of a fairly unique flight helmet. I picked up the shell at Pax River DRMO in 1987. It had no visor housing or any parts of any kind. For starters, it has a leather covered edgeroll. I put a VTEC liner in this as the helmet is transitional ie this ain't no APH-6 and not a PRK-37/P. There were no holes drilled for a nape strap, so I figure it didn't have one, and that means it used some type of form fit liner. It is a Navy Helmet (Red Rippers) so I figure VTEC. Note the square plugs in what looks like the APH-6 o-mask retainers. They do not come off, but they do pivot. I spent some time trying to match the paint on the visor cover and the standard EEK-4/P visor housing and visor fit the holes. Added APH-6 style comms (small hole in rear of helmet indicated an APH-6 style harness, older earcups and H-87 B/U receivers. This helmet may have used a prototype earcup with contact mics(?) in the earcup! But those aren't going to show up at Wal-Mart any time soon so I went conventional. Well, it's done and it only took 14 years.What do you think? cheers, Steve N.

Message 916:
I think this helmet is a prototype developed by Sierra Engineering. Chris turned up a sales flyer for the 756 series mask. The mask is a really strange hybrid of the MBU-5/P mask with a couple of unique twists. I am fairly certain this mask goes on my latest rebuild. I have actually seen pictures of this helmet in flight, but too far away to check the details. Pete Olsen has a shell like this only his has the earcups I mentioned. These earcups have been used in other programs most notably the HGU-35/P Navy flight Helmet from about the period (early 1970s) that I think this helmet was made. Cheers, Steve