Having started from scratch after World War II the Royal Danish Air Force used flying gear that more or less came with the aircraft they acquired. In the beginning Denmark bought a large number of surplus aircraft from the United Kingdom and consequently the flying helmets used were predominantly Type C leather helmets. From 1951 onwards came a large influx of US-built aircraft through the Military Assistance Program (MAP). Part of the thousands and thousands items delivered were P-1A and later P-3 and P-4 helmets. The P-helmets would eventually be in service until the late 1980s for technicians and non-regular crew members but already in the mid-1960s it was evident that a successor was needed for fighter aircrews.

From 1966 the Air Materiel Command Denmark (AMC DEN) searched the market for possible new fighter helmets, and during summer 1968 trials were conducted with a number of helmets. They included the USAF HGU-2A/P and its German Air Force adaptation, the HGU-2A/P(G), and also the British Mk.2A, and the US Navy APH-6A. As RDAF requirements developed to include the need for a double visor, all but the HGU-2A/P(G) fell through. In 1969 Sierra offered a custom fit version of the HGU-2A/P with one-piece ramshorn double visor housing. Field trials showed that custom fit helmets were more comfortable than helmets with strap suspension assemblies so preferences were clear from a user viewpoint. At the time, however, the custom fitting process was very time-consuming. A plaster cast had to be made of the pilot's head and sent to the Sierra factories where they would make the liner. It took 4-6 months for each helmet, and there was no way that the casting of liners could be done locally in Denmark. 

HGU-2A/P-D in the original configuration

AMC DEN suggested that the type of custom fit liner installed in the Swedish Type 112 helmet might be used for the HGU-2A/P but a closer look at the Swedish custom fitting system turned out to be less than satisfactory. As an alternative a Danish custom fitting system was developed, but the liners became too thick in comparison with the Sierra liners. Some of the aircraft in the RDAF inventory, notably the T-33A with its Martin-Baker ejection seats, had limited headroom under the canopy so the helmets had to be as low as possible. Yet another helmet type was tested in 1971, the Gueneau 316. It was low and had a well-functioning double visor system but it did not perform well in the Draken's noisy cockpit. Its noise attenuation was too poor.

The acquisition process was concluded in December 1971. From an operational viewpoint the custom fit double visor HGU-2A/P came out on top but the slow custom fitting process was not acceptable. Instead the HGU-2A/P(G) from Gentex was selected with its strap suspension assembly and a few additional modifications. Instead of visor lock screws the Danish helmets should have push-button visor lock knobs in order to get as little interference with the Martin-Baker seat upper ejection handle as possible. In this configuration the helmet was designated HGU-2A/P-D. 

The first helmets arrived in June 1972 and were introduced on the Saab Draken and Lockheed T-33A initially and later also on F-100 Super Sabre and F-104G Starfighter. Our Hunter pilots continued to use the P-4 helmet until the aircraft type was phased out in 1974. In late autumn 1973 two additional batches of HGU-2A/P-D helmets arrived. This made it possible to equip technicians with backseat status in fighter aircraft and later also C-130 loadmasters. The latter needed the helmet for added protection and noise reduction in connection with tasks involving flying with the rear ramp open. At high altitudes the helmet also provided fixture for an oxygen mask.

Far left, left and middle: HGU-2A/P-D configured for a C-130 loadmaster. The helmet is fitted with an MS22001 oxygen mask typically used when dropping parajumpers at high altitude. Right: The microphone is in stowed position with its cord secured by a velcro strip in order not to interfere with the oxygen mask. Far right: The microphone is down for low altitude tasks.

Problems with Martin-Baker seats
During ejection seat drill at Aalborg Air Base in July 1972 it was discovered that the upper ejection handle of the Mk.DQ-7 ejection seat got stuck on the rear of the HGU-2A/P-D visor housing when pulled forward. Several measures were tried to remedy the situation, initially by changing the ejection handle but it was not fully satisfactory. Two ALSE guys at Aalborg Air Base developed a longer visor housing that went all the way to the rear end of the ramshorn visor housing extensions. Initial testing of a metal sheet prototype looked promising so Gentex made a new protoype in plastic. This was tested in June 1977 and performed so well that the solutions had finally been found. The wheels of acquisition spun slowly but surely and the first production examples were received for approval in November 1978. Next summer the modification programme was initiated. Even if only the F-104 pilots had experienced problems it was decided that the modification should apply to helmets used on the F-100 also as this type was equipped with Martin-Baker seats as well.

The long visor housing developed for use with the Martin-Baker 
Mk.DQ-7 ejection seat

Custom fitting 
Tactical Air Command Denmark (TACDEN) were aware of the limitations of the strap suspension assembly, both in terms of comfort and ejection stability. The strap suspension assembly allowed the wind blast to enter the helmet during an ejection and more easily rip the helmet off of the pilot's head. In the late 1970s TACDEN became aware of a new custom fitting method which could be carried out in-country. In January 1980 a TACDEN delegation therefore visited the Norwegian air force who were in the middle of custom fitting their helmets. Here they saw how a polyurethane foam liner was cast directly on the user's head and subsequently covered with leather and fitted into the empty helmet shell. The thin rubber edge beading was replaced by a thick foam edgeroll covered in black leather. Only ten days later it was decided to go ahead with custom fitting the HGU-2A/P-D. At the same time it was decided to paint the helmets medium grey (FS26270). This was due to the fact that during exercises the white helmets often revealed the camouflaged low-level fighter-bombers to the high-level air defence fighters. [[04]]

Grey custom fit HGU-2A/P-D with snap-on edgeroll and grey plush on visor
housing and visor lock knobs to avoid scratching the canopy

The custom fitting tools were ordered from the US in May 1980, but the programme was delayed by slow delivery of tools and other materials. The Danish technical order was issued in October 1982 including procedures for painting and mounting grey plush on the visor housing. The latter was due to the fact that the canopies in both Draken and F-16 were scratched on the inside by the unmodified helmets in connection with manouvering.

All pilots had custom fit helmets but a limited number of HGU-2A/P-D helmets were kept with strap suspension assembly for use by non-regular backseat passengers, C-130 loadmasters and others who were issued a helmet for a shorter period.

HGU-"55"
The introduction of the F-16 from 1980 onwards pointed to another problem with the HGU-2A/P-D. It was too heavy for a 9G environment and the centre of gravity was comparatively high due to the visor construction. In March 1983 it was discussed whether the helmet might be modified to a configuration closely resembling the USAF light-weight helmet, the HGU-55/P. It was decided to test modify an HGU-2A/P-D by removing the visor housing and replace it with an HGU-55/P light-weight double visor. In order not to scratch the visors protective leather strips were glued to the helmet shell. Furthermore the oxygen mask connectors were turned downward to accommodate new J-bayonets instead of the usual T-bayonets but the helmet retained its original strap suspension assembly. 

Prototype of HGU-2A/P-D light-weight modification tested in 1983

Two months later the helmet was approved for operational test and evaluation following a satisfactory blast test in Germany. Four pilots took turns at testing the helmet until October 1983 and they were very positive. A few adjustments were made to the configuration and another test programme ran until June 1984. Again the result was positive so the modification programme was initiated in September same year. The helmets were brought up to nearly HGU-55/P standard with custom fitting, leather edgeroll etc, and in the USAF Technical Order they are designated HGU-55/P. In this article they are designated HGU-"55" not to confuse them with the factory-made HGU-55/P helmets. The HGU-"55" became the standard fighter helmet in all RDAF fighter aircraft (Draken, F-16 and F-104). 

HGU-2A/P-D modified into an HGU-"55" helmet . The black edgeroll,
earphone strings and cast oxygen mask receivers all reveal that it is not a
real HGU-55/P

HGU-2A/P-D becomes a helicopter helmet...
In late 1984 it was discussed how to improve the acoustic environment in the Royal Danish Navy Westland Lynx helicopters. There was too much noise in the intercom system. The Naval Air Squadron requested four Custom Fit HGU-2A/P-D helmets in February 1985 in order to see if they would be an improvement over the then standard SPH-3B helmet. The helmets were fitted and tested, and the intercom system rewired for thetest period. After thorough testing it was evident that the new helmets were a big improvement over the SPH-3B so AMC DEN recommended to TACDEN in May 1986 that the Naval Air Squadron should change helmet type. Also the Danish Army Air Corps had become unsatisfied with the SPH-3B and conducted a similar test of the HGU-2A/P-D custom fit with a similarly positive outcome.

...and becomes an HGU-26/P
As almost all flying units in the Danish armed forces tested the custom fit HGU-2A/P-D and were allocated the type it became a de facto standard helmet in Denmark. It was getting more and more difficult and expensive to get spare parts for the three-piece ramshorn visor housing so the side-acutated PRU-36/P visor was preferred as a substitute. Thereby the helmets effectively became HGU-26/P helmets.

HGU-2A/P-D modified to HGU-26/P with day-glo red visor housing for SAR
helicopter use

Initially the M-87/AIC boom microphones for helicopter use were mounted directly on the helmet shell but in May 1986 the life support technicians at Aalborg Air Base forwarded a proposal to change that practice. They proposed to mount the microphone on a modified oxygen mask T-bayonet, allowing the microphone to be mounted on the helmet and removed again as necessary. Hereby fighter pilots with status on light aircraft no longer needed two helmets. It was just a question of changing between oxygen mask and microphone as required.

The HGU-2A/P-D finally retires
The HGU-2A/P-D continued in service as either HGU-"55" or HGU-26/P until recently. For fighter use they were gradually being replaced by the real HGU-55/P because young pilots brought them home from flight training in the USA. The custom fitting procedure became obsolete because the chemicals for the foam were discovered to be environmentally unacceptable. The HGU-55/P helmets could be changed to the TPL-liner but that was not really an option for the original HGU-2A/P-D shells. The TPL-liner is fixed with velcro to a thin polystyrene energy absorbing liner in the helmet shell, in fact the same type of liner that used to be in the HGU-2A/P-D when delivered with strap suspension assembly. These liners, however, were discarded during the custom fitting process and now it was very difficult to get new liners for this helmet shell. Furthermore the shells were getting a bit long in the tooth for further modification. 
For helicopter and light aircraft applications the custom fit HGU-helmets were gradually replaced by SPH-5CF (Army Air Corps) and Alpha 221 (SAR helo, Naval Air Squadron, and light aircraft. C-130 loadmasters are equipped with HGU-55/P because of the requirement to equip them with the same type of NBC protection gear as used in the F-16