At the moment the HGU-55 is surely one of the most used flight helmets, worn by pilots in Airforces and Law-enforcement agencies worldwide.

This type of helmet shell comes with a large variety of visor assemblies depending on the task it is used for. It is capable of accepting the PRU-36/P dual visor assembly; a single visor housing assembly and the more commonly used single Snap-On visor. This last set leaves out the visor housing to reduce weight and giving it a lower profile. The different types of oxygen masks can interface with the helmet assembly by specifying the proper visor trim.

The helmet is normally sold without a fitting system. Fitting can be accomplished in the following ways:

• Gentex installed preformed Thermoplastic Liner (TPL®) system

• Foam fitting technique

• Fitting pads

The HGU-55G is the German designed dual visor assembly. This design is based on the PRU-36P set and has a different type of visor housing cover. It is curved to prevent parachute lines to get tangled in the housing.

The HGU-55/CE is the "Combat Edge" model. The helmet is part of a complete set of anti-g gear; the helmet has a bladder in the neck, which can be inflated during high G manoeuvres. Thus providing a better oxygen mask fitting. The CSU-17P pressure-vest also is a part of this gear together with the CSU-13/15P G-suit (speed pants). The MBU-20/P "Combat Edge" oxygen mask is used at this helmet.

The HGU-55P with PRU-36P is used, among others, on strategic bombers together with a set of nuclear flash goggles.

Standard configuration specifications 

Colour
The outside surface of the helmet shell is finished in lustreless grey polyurethane paint colour No. 36231 of FED-STD-595.

Shell
Made of fibreglass fabric moulded with epoxy resin.

Snap-On Visor
The Snap-On visor assembly attaches to the outside shell by snap fasteners on each side. Visor straps are secured to each side of the visor by two rivets and have strap adjustment buckles. Each helmet is provided with neutral grey and optional clear polycarbonate visors, which are, surface treated with abrasion resistant coatings.

Visor Buffers
Grey leather sections are cemented to the outside of the shell to provide a resting surface for the visor in the stowed position and to prevent scarring of the helmet shell surface when raising or lowering visor.

Energy-Absorbing Liner
Consists of an approximately ½ inch thick energy- absorbing Styrofoam, which reduces impact energy, transmitted to the head.

Gentex Thermoplastic Liner (TPL®)
An easily custom fitted, lightweight, comfort liner that is designed for use in conjunction with a Styrofoam impact attenuating liner. The TPL consists of layers of plastic moulded to create protrusions which, when the liner is heat softened, partially collapse to conform to the contour of the individual’s head. The entire assembly is lined with a removable, washable cloth cover next to the head.

Visor Stops
Two grey leather covered foam stops are cemented to the top of the helmet shell to prevent rotation of the Snap-On visor assembly off the back of the helmet during movement to the stowed position. 

Chinstrap Assembly
Consists of a chinstrap made of nylon webbing and a felt chin pad covered with cotton fabric. A buckle adjusts the length of the chinstrap. 

Nape strap Assembly
Consists of nylon webbing, pad and lacing. Should be adjusted to fit snugly against the neck at the base of the skull.

Integrated chin/nape strap Assembly

Newly developed is the integrated chin/nape strap assembly that is made of nylon webbing and features chin and nape strap pads covered with leather. Sliding clamps are installed on the left and right nape straps at the shell slots to allow individual adjustment.

HGU-55/P with integrated Chin/Napestrap

Communications
The HGU-55/P helmet assembly is normally equipped with an H-154A/AIC Headset which provides communications of high intelligibility under extreme noise conditions. The headset assembly components typically consist of the following components:

• MX-8376/AR ear cup assemblies, which include noise attenuating ABS plastic shell, earphone holders, and ear seals.

• H-143/AIC earphones having a frequency response of 100 – 5500 Hz and 19 Ohms impedance. 

• CX-4708A/AIC four-conductor cord assembly terminated at branched ends with pin type terminals and modified at the other end with a U-179/U connector.

Lightweight Oxygen Mask Receiver Kit
Consists of jaw/receiver assembly mounting screws, lock washers, back plate and spacers. Available in black and metal finish as well.

Lightweight Single Visor Modification
A single visor system is currently being developed to withstand a speed of 600 knot on ejection. This will probably similar in appearance to the visor system used on the HGU-68P.

Source: Gentex corp., Ron Kraan