VINTAGE ITEMS ARE NOT PERFECT THEY HAVE WEAR (NO RETURNS ON CONDITION REASONS), SO READ THE DESCRIPTION & HOVER\CLICK TO ENLARGE THE PHOTOS FOR DETAIL.  WE'RE IN THE WAREHOUSE MONDAY & WEDNESDAY TO SHIP YOUR ORDER KEEP THAT IN MIND.
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Authentic GENTEX US Military Aviation Vietnam War era Helicopter Pilot SPH-4 Helmet with Flight Bag

Helmet is certainly rare (Dated 1971) Late Vietnam War era original helicopter helmet that is  not complete, its missing a few parts but its intact with the liner. The helmet is marked size REGULAR on the white label attached to the interior of the helmet.  

Contract No. DSA100-71-C-1457 and Stock No 8415-144-4981.

Untested but CLEANED Lightly, I didn't fully clean the helmet, mask and bag just removed most of the surface dirt/dust. Normal Scuffs, staining or wear is normal from use.  Liner is mostly intact with some wear, including the right ear foam that surrounds the speaker has disintegrated.  Check All Photos and ask questions, im not an expert on helmets but ill try.  

One Clear rams horn visors is intact. Tint one is cracked with the other broken parts in the white plastic bag (last photo, see detail).

Oxygen MASK Size Medium, Type A13A has some dust present. The hose is distressed with holes or stress rips present. also probably missing some parts.

BAG, FLYING, HELMET, NYLON (DSA100-71-C-0642) Mfg by Raven Industries.  bags pockets are intact. No zipper present. Stains & Wear present, one interior small rip.  Faint Stenciling "REV-1-3" is present above the rip/worn QM Label. 

NO RETURNS
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INFORMATION ON THE SPH-4 FLIGHT HELMET
The Sound Protective Helmet-4 (SPH-4) is a derivative of the US Navy SPH-3 and was used by the US Army since 1970. The SPH-4 is a single-visor lighter-weight version of the SPH-3 and it replaced the two Army aircrew helmet then in use: The Navy-developed Aircrew Protective Helmet no 5 (APH-5) and the Army-developed Anti-fragmentation Helmet No. 1 (AFH-1). Both of these helmets were deficient in noise attenuation and retention capability. The SPH-4, which was specifically designed for sound protection, provided superior sound attenuation but the 1970 version provided no more impact protection than the APH-5A. As the sciences of crashworthiness and head injury prevention developed, it became evident that head injuries could be reduced by modifying the SPH-4.

Two types of head injury that might be prevented
continued to occur after the introduction of the SPH-4. One was concussions severe enough to prevent the crew member from saving himself from the crash site, and the other was skull fractures due to blows from the side (lateral). Furthermore, helmet retention proved to be a problem as well. A helmet can only protect a crew member if it stays in place and it turned out that one in five crew members involved in severe crashes lost their helmet.
The original SPH-4 had a shell made of fiberglass cloth layers bonded by epoxy. The inner polystyrene foam energy absorbing liner was 97 mm (0.38") thick with a density of 5.2 lb/ft3. The helmet was fitted with a sling suspension liner and had a nape strap with a single snap on each side fitting to studs on a retention harness.

The chin strap had a design strength of 150 lbs. The headset was mounted in 6 mm thick molded plastic ear cups with excellent sound attenuation characteristics. A regular helmet weighed 1.54 kg (3.4 lbs).

In 1974 the SPH-4 was modified with a thicker energy absorbing liner to reduce the risk of concussions. The new liner was 1.27 cm (0.50") thick and with the same density as the original liner. In 1982 the risk of concussions was reduced even further by manufacturing the energy absorbing liner with a lower density 4.5 lb/ft3. All in all the impact protection was improved about 33% over the original SPH-4 from 1970.

Nothing was done to the original SPH-4 design to reduce the risk of skull fractures due to blows from the side. The main culprit was the rigid plastic ear cups that turned out to be too strong in comparison with the skull around the ears. In case of a strong blow from the side the ear cup survived but the skull fractured. This problem was not addressed until the SPH-4B helmet was fielded.

Helmet retention, however, was improved. The original 1970 helmet had a chinstrap with single snap fasteners on each side and was designed to withstand a load of 150 lbs. In 1978 a double-Y chinstrap with two snap fasteners was incorporated to reduce failures. This chinstrap had a failure limit of 250 lbs based on the adjustment buckle strength.

In 1980 a third chinstrap was introduced. It was fastened to the ear cup assembly on one side with a small screw and T-nut, and the other side with two snap fasteners. This chinstrap had a failure limit of 300 lbs but some failed at 280 lbs.
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