This is an Apollo pressure helmet used by various astronauts during training sessions.
The Apollo pressure helmet was a blow-molded, clear polycarbonate shell with a molded bayonet base which was bonded to the helmet neck ring. The neck ring was the male half of the suit neck-ring assembly, and there were two configurations used on Apollo suits which were not interchangable. The earlier configuration was anodized blue, with the later configuration being anodized red.
A valsalva maneuver device was attached to the inner neck ring. It consisted of a rubber piece, molded to conform to the nasal openings, with an attachment mechanism and stiffeners.
A feed port was attached to the side of the helmet consisting of an inner and outer halves. The inner half included a port and gate valve that permitted the insertion of a water or food probe. The valve was spring-loaded and provided an air-tight seal when the probe was removed.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.