A History of the US Air Force P-series Protective Flight Helmets

  Of all the so-called 'hard' or 'jet-era' protective flight helmets produced in the United States since the introduction of enhanced protection requirements (the need for which was prompted by the use of the new turbojet engine to power military aircraft), the most interesting to me have always been the very first USAF designs from about 1948 through approximately 1959.

When the National Defense Act of 1947 resulted in (among other things) the emergence of the US Air Force as a separate service, the requirement for a pilot's protective military flight helmet had already been issued under the aegis of the Army Air Forces command and a design finalised. US jet aircraft, notably the P-80 Shooting Star (the first standard production American combat jet aircraft generated in large numbers), had been flying since about mid-1945. Just as the pilots of these aircraft lacked adequate head protection (necessitated by the higher performance of their machines), so too did the aircraft themselves lack any sort of vestigial provision for rapid, safe emergency egress (ejection seat systems), other than the traditional 'bail-out' over the side of a stricken craft.

Prior to the institution of a standard protective helmet design for use by all high performance aircraft crews, a number of unofficial and innovative designs were used by the earliest jet aviators--particularly by the pilots of the new Lockheed P-80A Shooting Star squadrons, whose personnel devised interim cockpit “bump protection” in 1946 by using the rigid fiber shells from WWII ‘tank crew’ helmets as an outer shell over existing soft AN-H-15 (summer), A-11 (winter), and A-10 (summer) flying helmets.

US Army Air Force Specification number 3277, drawing number 47R3184, resulted in the very first hard protective flight helmet, designated the "Type P-1 Flying Helmet". This was the result of Technical Order (TO) 13-1-37 / WF-(A)-O-17 Dec 1948, originating from Wright Field’s aeronautical laboratory. At about the same time, the first ejection seat systems were being introduced into jet aircraft; it is interesting to note that Army Air Force air research and development investigators had actually been concerned with and were actively looking into the pressing problem of how to exit a high performance aircraft safely, somewhat in advance of parallel concerns about protecting the head of jet fighter and bomber aircrewmen who flew the machines. Further, no less an authority on aviation medicine and flight physiology than the US Army Air Corps’ Dr. Harry Armstrong had much earlier (late 30s) investigated the possible benefits of rigid protective helmets for aircrewmen and found them ‘impracticable’.

Over the next 15 years (from about 1947) the Type P-1 Flying Helmet (substantially based upon pioneering studies undertaken by Dr. Charles Lombard) gradually evolved into its final configuration (known as the Type P-4B), a process that is best understood by modest familiarization with a profusion of complex USAF technical orders (TOs) that accompanied the updated specifications. Just how these changes regulated identification of the P-series helmets will be discussed briefly here, in hopes that this will enable those who are fascinated by modern flight protective headgear to more readily understand and identify the differences between all the variants of the important ‘P-series’ helmets, that were our first ‘hard’ protective headgear.

[One final note: Although an earlier type designated helmet was frequently upgraded to a subsequent specification, new production helmets manufactured at the precise moment a specification was in force were also given the same 'current type designation'. Thus, a type designation could be borne equally by both an older helmet (through T.O. upgrading) and a new one, by virtue of simply being a newly manufactured unit made to current specifications. This fact has created endless amounts of confusion, as regards positively and correctly identifying a particular P-series helmet today, and it is the chief reason why so many factors must be considered in deciding what designation a P-series helmet should properly bear in a chronological history.]

The Type P-1 flying helmet

This first hard protective helmet, the forebear of all US protective flight helmets today, came about as per the Wright Field Aircrew specification referenced above. Identified as Stock Number 8300-396400, this helmet was not intended to enable a pilot to survive a crash as much as to provide head protection within the close confines of the jet fighter (and bomber) cockpit. Thus, "crash-helmet" is a misnomer and actually somewhat misleading. "Hard-hat" and "brain-bucket" were vintage slang terms in favor among US pilots for these items, while "bone-dome" was a distinctly British (RAF) term in use, as the first hard helmets came into service on both sides of the Atlantic (the very first RAF rigid protective helmet was the Mk. I, which was worn with the RAF type “F” and “G” soft communications helmets underneath). There were many other slang terms for these items of 'personal equipment' that were somewhat less polite and the new helmets were at first not readily accepted by all air crews, who sometimes found them awkward to wear, visually restrictive, and uncomfortable to get used to. [There is at least one authenticated report of a pilot removing his early hard hat and using it to relieve himself, rather than leave the controls of a multi-engine type aircraft.]

The US Army Air Force Type P-1 Flying Helmet (for as such it was first known) was constructed of pressure and heat molded laminated cotton duck fabric that had been saturated with phenolic-resin (essentially similar to "Bakelite" materials). It was produced in one shell size (based closely upon the original “Lombard helmet” design) and used an internal head suspension sling of then-conventional design (similar to that used in Army infantry helmet liners and tanker crew helmets), consisting of a leather and cotton sling that could be adjusted through the use of laces at the rear to accommodate just about any size head. [Anecdotally, it is interesting to note that a study performed by the RAF in the 1950s found that pilots of fast, high performance (fighter) aircraft tended to have smaller head sizes than those who flew slower, multi-engine (bomber and transport) machines. We will stop short of engaging in any speculation about the size of the cranium in relation to the size of the pilot's ego, but the possibilities for formulating idle hypotheses are fascinating!]

The P-1 shell was issued in semi-gloss, off-white color paint, although it was not unusual to find them painted to suit the wearer's whims, with colorful personalised or squadron markings. The P-1 head-suspension sling crown pad was imprinted in white with "Army Air Forces" (this was very soon thereafter changed to "US Air Forces", and later “U.S. Air Force”, when the service became independent of the US Army in late 1947). While I have no absolute evidence that the earliest P-1 helmets were issued with a winged star decal on the outer forehead segment of the hard-shell (as in the manner of the "US Air Forces" decal found on the subsequent P-1A), my resources indicate that many did feature a decal of the traditional Army Air (Corps) Force winged star on a blue circular field (not unlike that used later, but without the lettering). Numerous photos and images from this period appear to provide evidence of this fact. The early P-1 head sling was identified by a woven black label that read "Sling Assembly for helmet, Pilot's Protective, Type P-1, Drawing no. 47D3185, Contract no. W33-038-AC1947S-(19413)". A manufacturer's name appeared in the last line and as per usual there were a number of primary subcontractors who produced the sling (among them Switlik Parachute Company, The Selby Shoe Company, The Bates Company, & the Joseph Beugelson Company). The P-1 head sling purportedly enabled a wide range of sizing adjustment, from about 6½ through 7¾, in use with the standard single size hard outer shell.  The prinicipal contractor for the first overall P-1 production run was the Paramount Rubber Company (manufacturer's of the shell).

The P-1 type sling, initially made of leather and OD cotton fabric, was later made of leather and nylon fabric (starting with subsequent TO versions of the P-1: P-1A/P-1B). Standard military white parachute riser cord was used to attach the sling to the hard shell and this is identified in the P-1 TO as being "Cord, Nylon, Type III, Spec no. AN-C-63", from which the inner core strands had been removed. The Type P-1 helmet did not have a fixed (riveted) chin strap as did later upgraded versions, but instead could be secured to the head if the wearer desired, through use of a chin cup that attached to the lowest of the snaps on the oxygen mask mounting tabs. Invariably, when an A-14 or A-13A mask was worn with the helmet, the mask itself served as a head securing mechanism. There was no nape strap on the P-1 helmet (as with P-1A/P-1B). Further, photographs we have seen of the original P-1 helmet show it to have a black rubber edge roll that is distinctively different from that fitted to the P-1A/P-1B helmet; this fact is substantiated by examination of actual surviving specimens. The P-1 helmet also had black-finished leather oxygen mask tabs, positioned on either side of the front face opening, each tab fitted with three screw-threaded snaps for securing either the A-14 Demand Oxygen Mask or the A-13A (later MS22001) Pressure Demand Oxygen Mask; later P-helmets used brown-finished leather tabs  that did not protrude through the edge of the beading and had off-white rubber edge rolls of a slightly different construction. A paper specification label was fixed to the inside of the hard shell in the area where a nape strap would later be added (in compliance with the P-1A TO).

The Type P-1 Flying Helmet as originally configured used the Type HS-38 headset, fitted with ANB-H-1 receivers; The helmet was subsequently upgraded to the HS-38A type headset, which used a slightly modified receiver element. This final headset type used (the HS-38A), was the type also used exclusively by the P-1A, P-1B, and P-3 helmets to come. All of these were fitted with the same kapok-filled, chamois leather covered earphone cushions found in all existing soft (leather or fabric) flying helmets, although the cushion attachment method differed from that used in the later P-1A TO upgrade. Active radio communications elements of the earliest original P-1 (initially using the standard ANB-H-1 WWII type electromagnetic earphone receivers) was identical to that in use on all soft fabric and leather US Army Air Forces flying helmets from WWII onwards.  Physically, the early ANB-H-1 receiver is entirely encased in black plastic and has screw-securing wire connectors; the later modified (HS-38A) receiver has a silver rung around the upper surface and has connections that are soldered on.

One important feature of the original P-1 helmet is found in the original manner of attaching the HS-38 headset cushions. The P-1 helmet initially used a system of earphone mounting retainer 'flaps'. These leather flaps were situated above and below the earphone hard-rubber holders on each side of the helmet and the cushions were secured in place with these flaps. This system proved less efficient than desired in actual flight use and in the subsequent P-1A design, earphone pads were attached via lacing at top (to the head sling harness) and bottom (to the bottom left and right hard shell). The original US stock numbers for the HS-38 and HS-38A headsets used in the P-1 helmet (and also in the subsequent P-1A) were "Electric Headset, 1790-207625000" (or 1790-207625500) and "Electric Headset, 1790-207626000". The early P-1 HS-38 type headset featured a single (high impedance) PL-54 type phone jack plug on the end of its com cord; initially there was no JK-48 microphone connector attached on the left side of the helmet shell that connected to the headset system loom. Later, when the HS-38A headset was adopted, the JK-48 microphone female connector was installed on the left helmet shell and constituted part of the headset communications loom & cord (today,  examples may be found with HS-38 headset installed using either the red PL-354--low impedance--phone jack plug or the newer U-75/U 'combination connector'). When the later HS-38A headset was adopted, the U-75/U communications connector replaced the single standard phone jack connector on the distal end of the helmet’s ‘pigtail’ communications cord (that exited from the rear of the helmet shell).  A few early P-1 helmets may have had the high-impedance HS-18 headset installed, in use with R-14 receivers. (The changeover from high impedance to low impedance communications systems in the Air Forces began during WWII).

The P-1 helmet, in its original, non-TO-updated issue configuration (with early HS-38 headset and ANB-H-1 receiver elements), is today very seldom seen, and P-1 examples that are still able to be found have inevitably been upgraded to later specifications. Most have long since disappeared as these helmets easily suffered structural failures in flight use and were taken out of service to be destroyed. Only a very few examples are now to be found and these were usually kept by the families of pilots to whom they were issued and whom had left the Air Force before the P-1A specifications were introduced. In terms of rarity, the Army Air Force Type P-1 Flying Helmet is on par with the original US Navy hard-hat design, the H-1 (of which also very few surviving examples are to be found today).

Although the P-1 specification (3277) is dated 1948, quantities of the new helmet were very limited at first and thus it was in short supply among US Air Force flying personnel at the onset, when introduced; photographs may be seen of P-80 pilots who were still occasionally wearing the soft tan ANH-15 & A-10 summer flight helmets, or the brown leather A-11 well, into the 50s (this was especially true for training applications, particularly in propeller-driven aircraft such as the T-6, the P-51, where the soft fabric helmets continued in standard use for many years). As might well be understood, the first P-1 hard hat issue was prioritised for first-line, high performance, jet fighter aircraft crews. Before many of the helmets had been issued, however, the P-1 was upgraded to newer P-1A specifications and therefore there were not great numbers of the original, unmodified design manufactured (we are presently uncertain of specific numbers produced). By the time the Korean War began, the P-1A specification had been issued and most of the hard helmets used by US Air Force personnel when that war began were either originally manufactured as P-1As or had already been upgraded to P-1A specs. Of additional interest from a historical standpoint is evidence (Col. Ralph Parr, quoted in the new book "Hot Shots: An Oral History of Air Force Combat Pilots of the Korean War", ISBN 0-688-16455-2) that highlights the scarcity of these original hard-shell protective helmets at the onset of the Korean "Police Action". Col. Parr states that in early June of 1951, as he entered active Korean combat in the new F-86 Sabre, he was using a "broken helmet" (presumably a P-1) that was held together with duct tape; he further states that these helmets were so scarce that several of the pilots in his squadron flew wearing the type of plastic football helmet that were in use in the early 50s by college football players (that the pilots themselves had brought over to Korea, or had sent to them from the US by relatives). This fact probably had at least something to do with a later decision to "reissue" the P-1A (leading to the P-1B type re-designation), after it was found that the older helmets were still needed by aircrews after the P-2 concept was cancelled.

The type P-1A flying helmet

The P-1 helmet, while it provided pilot basic protection, was far from perfectly configured for comfort and functional adequacy. As mentioned earlier, the 'flap attachment' provision for securing headset earphone receivers was shown to be somewhat less than desirable. Further, the lack of a secure chinstrap was another shortcoming. The forces encountered in high speed ACM (aerial combat maneuvering) required that the helmet remain fixed in place without skipping out of proper adjustment on the head. Further, with the adoption of ejection systems in the new jets, proper helmet retention and positioning was even more of a pressing requirement. Several steps were therefore taken to address these shortcomings with the introduction of a riveted (permanently secured) chin strap that went under the chin, rather than around it. Additionally, it was shown that an additional strap, fitted so that it ran crossways behind the cranial occiput, helped considerably to maintain proper helmet adjustment for the wearer. At this time, rubber framed goggles of the B-8 or M-44 type were commonly used with the P-1 to provide eye protection. Modifications subsequently taken to the basic P-1 shell included the addition of a fixed chin-strap, addition of a nape-strap, attachment of the HS-38A headset cushions with Nylon cord (Type I, spec No. AN-C-63) at the top of the cushion assembly (to the head harness) and at the bottom (to the helmet shell itself). A final modification involved upgrading of the oxygen mask leather attachment tabs, through removal of the original black finished tabs that protruded through the black helmet edgeroll, and replacement with light brown finished leather tabs secured to the inside of the helmet shell. The headset receivers (HS-38A) and communications plug (U-75/U) remained virtually  unchanged.

A P-1 helmet, thus modified, was specified as the P-1A. As was the usual practice, any older P-1s in use when the new spec came into 'standard' were upgraded to the newer specification, but any new units manufactured during this period were produced already incorporating these improvements into the new stock. Whereas the P-1 shell was made in one size that accommodated all heads, via adjustment of the head harness sling, the P-1A helmet shell was made in two sizes (small and large). This was an important innovation that made a proper, comfortable fit more readily achievable. The head harness slings used in each of the two shells again permitted more precise adjustment. Finally, a unique identifying characteristic of an original P-1 upgraded to P-1A specifications is a cross-hatched lacing of the front lateral edgeroll, where the edgeroll was sewn shut with heavy duty  thread after the original protruding mask suspension tabs had been removed and replaced.

The type P-1B flying helmet

The type P-1B Flying Helmet specification was created through a change in designation nomenclature only and the P-1A and P-1B helmets are otherwise identical in all respects. This came about as a result of a rescinded decision to take the P-1A out of standard service when the P-2 helmet design was cancelled; as demands of the new war in Korea required more and more of the new aircrew protective helmets, and in the face of a critical shortage of these items, the P-1A was re-introduced into standard issue with the designation P-1B (reference earlier remarks made by Colonel Ralph Parr of the 18th Fighter Wing--F-86 Sabre, Korea).

The type P-2 flying helmet

Although conclusive research has not yet been completed on this designation, the Type P-2 Flying Helmet was a limited, non-standard research prototype design developed by Wright-Patterson Aeronautical Labs as a 'proof of concept' application of the new US Navy approach of utilising a soft fabric (nylon) helmet to hold the communications headset under a hard outer protective shell. The Navy experimented with this idea and replaced its original H-1 helmet (and the subsequent H-2, which was somewhat similar) with their new H-3 design (using the two-part helmet concept) that consisted of a two-component (soft inner/hard outer) assembly. [The Navy H-3 was in turn replaced by a slightly modified version known as the H-4, before the original integrated assembly approach was once again adopted in the short-lived H-5 integrated helmet. After a short period of service, the H-5 was replaced by the new APH-5 in 1958]. The USAF P-2 design is shown in several Wright Patterson Aero Lab photographs as being a hard P-1 type white phenolic resin impregnated cotton duck shell used over a conventional USAAF type A-10 khaki poplin flying helmet (to which the communications headset was configured). Presumably, the headset used was the HS-38 or 38A headset and the photographs referred to show an A-13A/MS22001 type mask in use that is attached to snaps on the leather tabs of the A-10A helmet. Otherwise, the outer rigid shell features the same conventional design P-1A type leather/nylon head suspension sling, fitted so as to accommodate the slightly extra protrusive bulk of the inner A-10 helmet. Although to this date, these facts have not yet been confirmed to me officially (research on the mysterious "P-2" in still underway), these hypotheses appear to be reasonably certain, based upon several archival photographs referred to earlier. Seemingly, for unknown reasons the Air Force found that the Navy concept was unsuited for Air Force use and the original one-component, integrated design of the P-1A helmet was kept and simply updated on a continual basis until about 1959, when the entirely new HGU-2/P helmet was introduced. [Of interest is the fact that the RAF initially also used a two-part helmet design in their Mk.I, which paralleled the US Navy’s originally rigid helmet approach.]

[One additional fact has emerged that has led to some confusion among a few individuals who have erroneously identified P-1A/B helmets as being of P-2 specification. This is the fact that immediately prior to the US Air Force’s decision to cancel the P-2 production, an unknown number of head harness slings with woven labels identifying them as “Head harness, Type P-2”, were produced. When the P-2 helmet order was cancelled, these “P-2” head harnesses were used as replacement units in existing P-1A and P-1B helmets. It is important to reiterate that the P-2 helmet was never produced or issued; these P-2 harnesses are not to be misconstrued as being evidence that the helmet they have been used in is a genuine “P-2 helmet”.]

Available information shows that the production contract for the never to be produced two-part P-2 helmet was given to the Paramount Rubber Company, the same contractor that had produced the original P-1 to US Army Air Forces specifications.

The type P-3 flying helmet

In 1950, a further modification was undertaken to add wind-blast protection to the P-1 style helmet. With improvements in aircraft ejection seat capabilities, pilots no longer needed to attempt a manual 'bail-out' over the side of a stricken aircraft. Speeds and performance capabilities were simply too great to insure aircrew survival in such situations. The old B-8 rubber framed goggles were thus replaced by a new rigid side-latching external visor assembly. Rubber goggles tended to be blown off of the helmet in an ejection and the new visor assembly, while still far from perfect, went a long way towards helping insure helmet and mask retention against the effects of severe wind-blast that were a routine hazard of emergency ejection at high speed. This early rigid, vertically articulated visor had two secure positions--full up or full down. It used a unique sort of ratcheted pivot mechanism with each one of the two latches securing to a pinned triangular mounting plate positioned roughly at about the area of the helmet's temple on both sides. Springs were used to pull the helmet visor into the full-up position when it was lifted free of the temple pins by positive forward and upward hand motion. This visor assembly was designated the PN 51C3632 assembly. Of central interest is the fact that any P-1 helmet (P-1A or P-1B) to which this rigid visor assembly was added, automatically became re-designated as a P-3 helmet. The P-3 was otherwise identical in all respects to the P-1A and P-1B helmets. As before, all older P-1A/B helmets were upgraded to the new type designation as circumstances permitted and helmets manufactured after the TO change came into force were produced by assembly at the factory.

An item that is worth noting in passing is that due to the constraints of the Korean War on supplies in the combat areas, repairs to the headset cushion assemblies of P-1 and P-3 type helmets were frequently made using salvaged or cut-out kapok-filled chamois leather-covered cushion 'doughnuts' removed from AN-H-15 and A-10 type fabric helmets. Although the cushions were not absolutely identical in every respect to those used in the rigid P-series units, they were nearly so, and this explains the discovery of what appear to be AN-H-15 & A-10 type ear cushion units fitted to early P series helmets that were used in and around Korea from 1951 through 1953. For this reason it is therefore not technically 'incorrect' to “restore” a helmet by replacing old, worn-out P-helmet earphone cushions with AN-H-15 and A-10 type units today, when rebuilding these early items of headgear. There was, after all, an expedient historical and practical precedent for the practice!

Because of its superior wind-blast protection, and also because of its additional sun-glare protective function, the Type P-3 Flying Helmet was mandated for use in all high-speed, high performance jet fighters and bombers. Somewhat later slight modifications of the basic 'side-latch' rigid external visor were adopted. The differences between the original version and the later two versions are not readily apparent until helmets fitted with each version are compared side by side. The principal modification was two-fold: the protrusive 'tab' located at the top of the visor mounting bar was done away with and the length of the side latch securing arm was slightly lengthened. In the case of the latter modification, this small change permitted the visor to swing up completely out of the peripheral visual area of the pilot's face, whereas the original ratchet-securing articulation permitted part of the lower lens on both sides to slightly obscure the upper periphery of the pilot's field of view. [It is worthwhile to note that the rigid shaded visor lens used with the P-3 type side-latched visor came in three sizes (small, medium, and large); the required size was determined as being equal to the distance between the top center of the visor and its lower nose-bridge point and had nothing to do with the curvilinear lateral measurement of the visor lens itself (as has been sometimes assumed). The correct visor size for a wearer was established with a ruler, after the correct mask had been fitted to the helmet. The visor mounting bar assembly was referred to in official T.O. references as the visor "yoke".]

Other small changes that were incorporated into all the P-helmets at various times in the early to mid 50s included replacement of the original riveted chin-strap with a slightly modified one, addition of a chamois-covered, wool-cushioned pad to the helmet's chin-strap, replacement of the leather oxygen mask attachment tabs with ones that made the snaps more accessible, and introduction of a slightly newer head-harness sling. Overall, however, the P-1A through P-3 helmets were virtually identical for the most part and only the new rigid external visor distinguished the P-1 series from the P-3 series helmet, for all practical purposes. All the early P-series helmets including the P-1 through the P-3 helmets used the HS-33, HS-38, and HS-38A communications headset assemblies (AN-AIC-1), with characteristic chamois-covered, kapok-filled earphone cushions. The next major upgrade would come about with the introduction of the Type P-4 Flying Helmet specification in late 1955. [Of interest is the fact that chin straps found on early versions of the P-1A helmet—especially original P-1 helmets upgraded to P-1A standards--included olive drab cotton duck variants, as well as the white cotton duck straps that are more common.]

The type P-4 flying helmet

The USAF Type P-4 Flying Helmet specification came about with the need to make helmet headset communications and oxygen mask dynamic microphone compatible with new aircraft intercommunications sets of the AN AIC-10 standard. The year of 1955 saw a number of upgrades undertaken to modify the P-series flying helmets. In early 1955 all earlier type P-series helmets (P-1A/P-1B, and P-3 helmets) were updated with the new H-75/AIC headset. Originally, the A-13A/MS22001 masks had used, as did the A-14A mask, the ANB-M-C1 carbon element microphone. With the introduction of newer noise-canceling dynamic microphones (M-32/AIC mask microphone assembly and the boom-type M-33/AIC assemblies that were used through the early Vietnam period), the new H-75/AIC headset system was added to the earlier P-series helmets (the earlier HS-38 headsets and ANB-M-C1 microphones were not compatible with the new aircraft communications systems coming into use). Unlike the original HS-33/38 type earphone cushion design, the new earphone cushions used more modern cushioning material (open cell foam rubber, protected by a black 'Hypalon' external skin). More importantly, the new system did away with the original and simple system of using sponge rubber half-rings to custom adjust the HS-38 kapok-filled chamois cushions to the pilot's ears. The new earphone cushion assemblies were spring mounted and tethered to short nylon strings which protruded through the lateral helmet walls to be secured over a rubber lock-nut and snubber bar. A type U-93/U com connector was fitted to the helmet communications 'pigtail'. Shortly thereafter (in July 1955), a slightly modified H-75A/AIC headset replaced the H-75/AIC assembly (TO 14P3-4-508). All helmets modified accordingly with the new communications assembly were type-specified to the new P-4 designation.

In 1955, all P-series helmets were officially upgraded to the new P-4 type specification, which called for the replacement of earlier headsets with the H-75B/AIC assembly. An earlier P-3 helmet, thus updated, became designated as a Type P-4 Flying Helmet. P-4 helmets, newly assembled were delivered directly from production runs with the new headset assembly. The P-4 helmet still featured, however, the early original heat/pressure molded phenolic resin saturated cotton duck shell. As before, the new headset used a rear exiting 'pigtail' communications cord, but the com connector was designated Type U-93A/U. Also, in keeping with the earlier P-1A/P-1B system, the P-4 helmet was made in two sizes (small and large) only. A type JJ-055 microphone connector was an important feature of the new headset specification, the adoption of which required use of a slightly larger rubber 'boot' that was stitched to the left rear area of the helmet shell to replace the older connector and boot (this is simple way of determining at a quick glance whether an early P-series helmet has been TO upgraded to later P-4 type specifications; an original HS-38 type mic connector would feature the smaller elongated "U" type rubber connector boot for the earlier JJ-048 connector).

At about this time (1954-55), due to all the TO changes that appear to have been introduced to the P-series helmets, an already somewhat confused type designation system becomes slightly more so. Another change resulted in P-1A/P-1B helmets used without the side-latch visor assembly being re-designated the MB-4 helmet. It is important to note that the MB-4 configuration (which was otherwise identical to the P-4, except that it lacked the rigid external visor) was apparently intended for use in non-high performance aircraft, such as slower, multi-crewed bombers, transports, and utility aircraft, in which the extra protection of a wind-blast visor was not needed and in which the protruding mechanism itself might pose needless range-of-motion encumbrances on a crew flight deck or within a flight station. Here, the confusion increases further, as the external visor assembly was frequently added to the MB-4 designated helmets arising from individual pilot preference, although the rigid wind-blast visor was not standard to the MB-4 specification. Thus, surviving specimens of both the MB-4 and the P-4 can both be found today with the visor assembly installed...a situation which has created some consternation on the part of helmet collectors, flightgear archeologists, and life support historians. However, despite this apparent incongruity, the MB-4 and P-4 helmets were given mutually distinct PNs and other identifying nomenclatural numbers, according to the TOs. TO 14P3-4-508 dated 11 Jul 55 specifies that "...any P-1A/P-1B helmet updated with the newer H-75/AIC headset system (and lacking the visor) will be designated as Helmet, Flying, Type MB-4", whereas "...any P-3 updated to the (new communications) specification will be thereafter designated as Helmet, Flying Type P-4". One final observation here is of interest. The TO also specified that any helmet thus modified or updated would have the original helmet shell identification tag covered with a new, self adhering tag identifying the assembly by its updated type. Although some helmets modified accordingly will still have this added tag in place, in some cases it has been removed by collectors interested in learning what the original shell label specified. (Unfortunately, the label has not been placed back on the shell in compliance with the strictest spirit of authenticity, in many cases.)

Thus, all the early P-series helmets including the basic rigid helmet and suspension systems of the P-1, P-1A/P-1B, P-3, P-4, and MB-4, were essentially identical to each other, with only small, technical differences in communications assemblies, subcomponent items, visors, and accessory parts variations. A P-1A or B helmet with the new side-latching rigid visor added became a P-3 helmet; a P-3 to which the new com system had been installed became a P-4.

The type P-4A flying helmet

In June of 1957, a new type visor yoke assembly was retrofitted to all earlier P-4 helmets. This consisted of the new visor mechanism that, while quite similar to the original rigid external visor assembly in superficial appearance, did away with the side latching design in favor of a tracked visor securing system actuated by grasping a central rubber knob and pulling the visor down into position. Two positions were permitted, full up and full down just as in the original design, but the new knob actuation was grossly simpler and somewhat easier for a pilot to accomplish quickly and positively. This new assembly was fitted to all external visor equipped P-helmets in place of the side-latch design, and there were two yoke sizes (small/PN 51C3632-1, and large/PN 51C3632-2) and three visor sizes (small, medium, and large). The P-4A specification was applied to all P-4 helmets thus retrofitted, but newly assembled P-4A helmets made use of the new fiberglass shell material that replaced the earlier phenolic resin and molded cotton duck material.

T.O. 14P3-4-1 dated 30 Apr 57 states that “…with the exception of the new center-track actuated rigid external visor, type MB-4 and type P-4A helmets are identical” (although the MB-4 sometimes had the visor added by bomber crews that used them, as before). Further improvements to newly manufactured P-4A helmets included the incorporation of ensolite type sponge pads lining the internal surface of the new fiberglass shell at front, rear, and crown (replacing the original, older open-celled sponge rubber used in early P-series helmets). As before, the headset used remained either the H-75A/AIC or H-75B/AIC specification, but the communications “pigtail” ended in the U-93A connector (similar to the U-93). A further additional change that was instituted with introduction of the new P-4A TO specification was inclusion of an additional shell size: Extra-Large. The USAF PNs for the P-4A shells were as follows: Helmet, Flying, Type P-4A, Small, PN 56D3508-1; Helmet, Flying, Type P-4A, Large, PN 56D3508-2; Helmet, Flying, Type P-4A, Extra-Large, PN 56D3508-3. MB-4 helmets were, of course, originally P-1A/P-1Bs, and their PNs were: Helmet, Flying, Type MB-4, Small, PN 54D3733-1, and Helmet, Flying, Type MB-4, Large, PN 54D3733-2. Visors for the three P-4A shell sizes were: Visor, Small, PN 51D3643-3; Visor, Medium, PN 51D3643-2; and Visor, Large, PN 51D3643-1. In simple summary, P-4 helmets to which the new center-track visor system was added became P-4A specification.

The type P-4B flying helmet

In 1959, a final TO P-helmet specification was issued that consisted principally of a change in the headset communications cord assembly. The P-4B helmet specification did away with the helmet communications 'pigtail' cord and substituted a new helmet cord assembly designated the CX-4708/AIC. This allowed the entire earphone and mask microphone communications system to be integrated into the aircraft radio and intercom systems via the oxygen mask communications cord  connecting the new H-149/AIC system headset. The active earphone receivers were updated to H79/AIC specs and the previously used, spring-loaded earphone cushion assemblies were done away with. Instead, in what would appear a “retrograde progressive” move, the earphone cushions were again secured to the rigid helmet shell at upper and lower sections in a manner not unlike the attachment system used in the P-1A/P-1B helmet. Foam pads were again used to adjust the cushions to the pilot's ears. This system would also be used in the following, new generation helmet (the HGU-2/P), before a return to a slightly different type of spring loaded earcup would return in the even later HGU-2A/P helmet. [The reason given for replacement of the heli-coiled “tophat” spring-loaded earphone system in the P-4A was that some crew had apparently sustained severe injury in crash situations involving a crushing lateral impact on the helmet; in certain instances, it was found that the metallic spring units and their screw retainers could actually be driven into the cranium, resulting in non-survivable head injuries to the temporal skull.]

While older P-4A helmets were updated in the field to the new P-4B specs, newly manufactured stock featured all of these refinements directly from the factory run. The external rigid visor was unchanged from that used on the P-4A. Newly manufactured P-4B helmets had no rubber plug-filled circular orifice at the rear of the shell (where a former com cord pigtail exited); older P-4A helmets that had been updated by squadron personal equipment/life support techs to P-4B specs featured a black rubber plug in this area. As before, the JJ-055 mic connector jack (outlet on pilot’s left) was used in the helmet earphone loom.

The early H-149/AIC headset, originally used with the late model P-helmets (B) and with the first of the HGU-2/P helmets that replaced the P-series, was used with the new CX-4707/AIC series oxygen mask hose routed communications cords (these last specification cords are still in use today in slightly updated configurations). [It is not altogether uncommon to find that a P-4A specification helmet was occasionally ‘created’ simply by cutting and removing the ‘pigtail’ communications cord, a modification which resulted in the functional equivalent of the new P-4B wiring loom!]

Notes on the P-series visors

The P-series first, second, and third model visors.

As far as the P-series visors go, there are actually four definitive variations in the P-series evolution. The VERY early (original) P-series visors (1^st, 2^nd, and 3^rd design) featured several characteristic design details that subtly set them off from the 4th and final refinement. The earliest (original) visor yoke used a side-latching method of securing the visor, but had no “J-hook” extensions to hold the visor in the ‘down’ position. The 2^nd and 3^rd style side-latching visors did have these distinctive “J-hook” latching arms. Both of the 2^nd and 3^rd style visors used successive evolutions of what I have come to term the "side-latch J-hook" visor yoke, in that they lacked a center track (as used in the P-4A visor and TopTex systems) and secured the visor in an up-position by spring activated reflexive retraction, and down by the positive engagement of the short "J" arms (on the lateral aspects of the visor bar) onto the pins protruding from the temporal helmet visor-mount fixtures. The differences between the first three visor yokes may be seen in the accompanying photographs. The 2^nd and 3^rd ‘side latch J-hook’ yoke visor assemblies may be differentiated from each other by virtue of the short throw of the 2^nd design’s lateral "J" arms (about 1", versus 1&1/4" on the succeeding version). The short throw of the 2^nd design’s "J" arms was found to result in the protrusion of the lower visor edges in the upper peripheral field of the pilot's vision; this constituted a slight, but significant visual distraction--not something, as the popularity of the much later HGU-55/P helmet and the HGU-33/P cutaway visor-cover has borne out, that pilots welcomed in heated air-combat engagements. Further, the protuberant upward thrusting square flange on the visor bar on visor yokes 1 and 2, although intended to serve as a convenient gripping point for visor hand actuatio, was found to snag on things (such as parachute riser shrouds) and also scratched canopies. The 3rd version of this original P-series visor came with this protuberant flange removed (close examination of one such later visor bar will reveal only a short stub where the flange used to be); furthermore, longer "J" arms on the side-latching mechanism (about a quarter of an inch longer, but enough to do the job quite effectively) of the 3^rd design allowed the retracted visor to secure in the open-position much higher on the helmet's forehead section--this removing the offending lower visor field's peripheral distraction up and away from the pilot's fields of vision. In the field, the early original visor yoke was sometimes field modified with addition of the longer "J" arms, and the upward thrusting "grip" flange was often filed off to a nub. [There were also two distinctly different, although superficially similar appearing helmet mounting attachment plates upon which the visors swiveled. Very few of the earliest type with a top pivot extension (rather than a bottom pivot, as found on the last type plate) remain today and almost all examples found on surviving early helmet specimens are of the second and finally adopted type.]

[One final observation is salient here. The original ‘side-latch non-J-hook’ visors featured a curious circular perforation pattern in the external yoke bow. This may be clearly seen in some of the earliest images shown in Air Force technical publications. The reason for this unique pattern of holes in the outer visor yoke is still unknown at this time, but subsequent to this appearance, the later yoke bows on all P-helmets are noted to all have been uniformly constructed of smooth metal (aluminum).

The P-series 4th model visor

The 4th and final P-series visor design used the new “center-track system”, which is common to all P-4A and P-4B helmets (the early side-latch visors were used only on TO upgraded P-1A and P-1B helmets, and on P-3, and P-4 helmets). It retained the familiar springs on both sides for full up visor retraction, but relied for securing in full down positioning on insertion of the visor's spring steel mounted and rubber knobbed ball-pin int