Army aviators' mask for chemical warfare defense

Army aviators must be able to safely operate a highly complicated and expensive piece of equipment under all conditions. This includes operating the aircraft in a nuclear, biological, and chemical environment. Adding the protection required to defend against chemical warfare agents restricts aviators and hinders their ability to fire and maneuver safely. The perfect aviator's mask is one that provides the needed protection, does not limit peripheral vision, adds no stress to breathing, and causes no heat stress. The search for this mask has been a long one. As time and technology advanced, better and better protection was devised. This article discusses the history of the Army aviation mask development.

World War I

With the onset of chemical warfare and the United States' entry into World War I, Army leadership ensured that all soldiers and working animals were given basic protection. However, masks had not reached the stage where special ones could be developed. If an airplane pilot needed a mask, he wore the same small box respirator (SBR) as the foot soldier. The first mask, the SBR (and its derivatives the Corrected English [CE] mask and the Richardson, Flory, and Kops [RFK] mask), provided the necessary protection, but did so at the cost of comfort, vision, and heat stress. One can only imagine how well a young pilot could fly with a clamp on his nose, mouthpiece in his mouth, and tunnel vision through yellowing eye lenses. Fortunately, pilots were kept away from gas attacks and only needed masks if their aerodromes were attacked. By the end of the war, the Chemical Warfare Service had an outstanding mask ready for the soldiers--the Model 1919 (later the Mark I or MI).

The Model 1919 was the finest mask constructed for American soldiers during the war. Unlike the earlier SBR, CE, or RFK masks, it used the mask facepiece to keep agents out of the lungs instead of a noseclip and mouthpiece. This resulted in a more comfortable mask which was less fatiguing for the wearer. This innovation was first issued in the French Tissot mask and used in the American Akron-Tissot and Kops-Tissot-Monro masks during the war. The Model 1919 used the best design features of all the masks. The facepiece was designed to fit the majority of soldiers whose faces had been measured during wartime research. With a superior mask for general use, the Chemical Warfare Service scientists could start designing masks for specialized uses.

The Army Air Corps/Forces Era (1920s to 1940s)

Edgewood Arsenal developed an airplane pilot mask in 1923. It had a standard Mark I facepiece with a quick detachable union on the hose and an angle tube (where the filter hose connected to the mask). The pilot could wear the mask without the canister, except when actually entering a contaminated atmosphere, when, as he flew the biplane through the sky, he could attach the hose to his facepiece for protection. This same connector could be used to connect to his oxygen tank when necessary. To eliminate the complicated hand movements to attach the hose, the Chemical Warfare Service developed a four-way valve to allow the pilot to wear his mask and choose his air source--fresh, filtered, or onboard oxygen. Never adopted or procured in quantity, this mask remained a curiosity. The first airplane pilot mask solved the protection problem and made progress on comfort, but it still limited vision and increased breathing resistance and heat stress.

Sensing the need for a true aviator's mask, a formal requirements document was issued in 1933. In 1934, a project specification for an airplane pilot's gas mask was approved. This specification was forward-looking: a molded or semimolded facepiece with pilot's goggles for eye lenses and a canister with a four-way valve, an air scoop to obtain forced air to filter and prevent lens fogging, and connecting tubing. Most of the mask's system (canister, valve, scoop, and connections) was to be permanently mounted on the airplane.

To meet the product specification, many mask modifications were tried, but none were fully successful. Problems encountered included mask fit, eye lens fogging, mask complexity, vision clarity, communications, and oxygen supply. Designers tried lining the mask with chamois to solve the fitting problem. Unfortunately, this modification made no conclusive improvements to the mask fit or protection.

Eye lens fogging was a major problem, and designers made numerous attempts to solve the problem in the early experiments. Finally, in 1941, the nosecup was introduced. This isolated the nose and mouth from the eyes, and fogging was prevented down to 8 degrees Fahrenheit. A nosecup was used in all future models of the airplane pilot's gas mask. The nosecup was also added to infantry masks, starting with the M3.

To solve the mask complexity problem, engineers at Edgewood Arsenal tested a mask fitting the 1934 specifications against a lightweight service mask and a training gas mask. Both masks were altered to allow a rubber hose attachment. The specification required the pilot to have an "escape canister" available for emergencies and a quick-disconnect attached to the four-way valve. It is not surprising that pilots preferred the training mask assembly because of its simplicity and light weight.

Pilots must be able to see clearly with a wide field of view. Under normal circumstances in the 1930s, they were issued pilot's goggles. These ground-glass lenses worked well in the standard goggles but not in their gas mask. This was due to the mask design. Designers tried flat lenses to increase the field of view but had no success. Use of optically ground goggle-shaped lenses was not an improvement over standard triangular-shaped lenses. So, tests continued. The three methods tested to provide communications capability were diaphragm facepieces, throat microphones, and integral microphones. Neither a diaphragm facepiece nor a throat microphone was fully successful. By the end of World War II, an integral microphone was still not developed.

The original specification for a pilot's mask included a four-way valve for various types of air supply--filtered air, unfiltered air, and oxygen mixtures. This added weight and bulk to the mask system. It was ultimately replaced with a small tube that was part of the inlet valve to the filter. Masks with the filter inlet tubes included modified training and service masks. In World War II, designers modified a lightweight service gas mask with standard Air Corps oxygen-mask couplings so that it could be used as an oxygen mask.

During the war, 50 modified lightweight service masks (E41R182-M10-6) were developed and sent to the 8th Air Force in England for field trials. Pilots also tested an unmodified M5- 11-7 assault gas mask. Tests showed that the M5 worked. However, some pilots found side vision restricted, the side canister uncomfortable, and mask carrying an annoyance. The test report recommended halting further development of a pilot's gas mask because of its limited use to the aircrew The Army Air Force felt that pilots would use the mask when boarding the aircraft and taking off but not during flight because the standard oxygen mask was available. In 1945, the military characteristics were revised--attaching to an oxygen supply was eliminated. In fact, the revised characteristics focused primarily on protection, weight, size, visibility, and comfort. These characteristics were similar to other programs, so the military requirement was cancelled in 1946. The Air Force became a separate service in 1947, and Army interest in a n airplane pilot's (later termed aviator's) gas mask diminished for a time.

Enter Army Aviation (1950s)

In the 1950s, the Transportation Corps (that had proponency for aviation at the time) identified the need for an aviator's protective mask. The Corps's leadership recognized the need to protect the aircrew if they were forced to land on contaminated terrain. Searching for a quick solution from procured and developmental masks, they found the M14-series mask (then under development) to be the best solution to their problem. The original M14 mask, modified to allow use of an appropriate microphone, was not acceptable in its original configuration but showed potential. The developmental aviation mask was called the E75 (Experimental Mask Number 75). Further research introduced refinements to the M14 mask such as a nosecup and wider eye lens. Exchanging the microphone for one compatible with the AN/ARC-44 aircraft radios produced an acceptable aviator's mask. The E75R5 was adopted as the M24 mask in 1962 after the fifth revision (R5).

The 1960s

The M24 mask was the first true aviator's mask the United States Army issued. It was adopted 28 years after the formal requirement document was issued. The mask was issued with an M7 hood, M3 winterization kit, M1 antifogging cloth, M1 waterproof bag, M8 adapter (to attach mask to an oxygen system), and M13 carrier. It was very similar to the M25A1 protective mask (adopted in 1963). Some M25A1 masks were converted to the M24 standard in the 1990s. An easy way to tell the M24 mask from the M25A1 mask is that the microphone connector of the M24 was a two-prong male and the M25A1 was a two-hole female. The M24 mask fit the bill and protected the aviators; however, research to find a better mask continued.

The 1970s

Entering the 1970s, the Army had four standard protective mask types: Ml7/M17A1 (general purpose), M9A1 (special purpose), M14A2/M25/M25A1 (armored vehicle), and the M24 (aviator's). Using a common mask system for all would simplify logistics and save money. Thus, the Army sought to develop a common mask system--the XM-29. This one mask used a common facepiece for all variations. It was a one-piece, injection-molded silicone-rubber construction with a protective coating for scratch and agent resistance. It used a screw-mount filter canister that mounted on either the mask cheek (right or left side) or on a hose. There were two voicemitters--one on the side opposite the filter attachment and one on the front. It also had a hose permanently attached to a separate filter fastened to the belt or chest of the aviator. The XM-29 eye lens had a tendency to "frost" but could be corrected by scrubbing it with a mild cleanser. However, problems with the lens coating led to the Army focusing on the XM-30 series develop ment. The XM-30 was effectively an XM-29 with a separate glued-on lens.

The 1980s

The XM-30-series masks used separate designations for each mask variant. The XM-33 was the aviation mask designation. The XM-33 differed from the basic XM-30 in that it had an external outlet valve, cover-mounted microphone and a hose-mounted filter. There were some developmental problems with attaching an eye lens to the silicone facepiece, but work progressed until 1981, when Senator William Proxmire bestowed one of his famous "Golden Fleece Awards" for a perceived waste of taxpayers' money. Shortly thereafter, the Army determined that the XM30-series masks were unacceptable and initiated the minimum-change, minimum-risk XM-40 program.

The M40 program was initiated to modernize the Army mask as quickly as possible. The objective of the M40 program was to combine the best elements of the M17 and XM-30 programs into a new mask for the military. Several versions were called for, including an aviation mask-the XM-41. Scott Aviation, ILC Dover, and Avon submitted masks for the program. Unlike the XM-33, the XM-41 had an internal nosecup-mounted microphone. Scott's design won the competition, but the XM-41 was eliminated because the mask lacked the necessary field of view the aviation community required and could not be used with night-vision goggles. The engineers, scientists, and technicians within the Individual Protective Division of the Chemical Research and Development Center were continuing with technological research to prepare for just a contingency. They created a new program, eventually designated the XM-45 mask program, to develop a new general aviator's mask. Another mask program was already in place to develop a special mask to ful fill the requirements for the new and exciting Apache program--the XM-43 Apache mask.

Adopted in 1986, the M43 aviator's protective mask was a radical departure from previous masks; it was unique among the Army masks. It had a form-fitting bromobutyl/ natural rubber face-piece with lenses mounted close to the eyes and an integral chemical-biological hood. The mask was held on the aviator's face by a skull-type suspension system. A powerful, portable 4-cubic-feet-perminute (cfm) blower unit forced air through two C-2 filter canisters and a hose to an inhalation air-distribution-system assembly. This assembly regulated the flow of air to the oral-nasal cavity, lenses, and hood. The aviator could adjust airflow to his head, keep the eye lenses clear, and still get enough air to keep the mask at overpressure. By including a blower unit, this mask became a powered air-purifying respirator and had a higher protection factor than many negative-pressure respirators (standard masks). The blower unit was designed to mount on the aviator's seat while in flight and draw power from the aircraft. In an emer gency egress, the dual filters could be pulled out of the cockpit-mounted motor blower. A pressure-compensated exhalation valve assembly helped the aviator maintain overpressure in the mask/hood and had a built-in electronic microphone. Finally, for the first time, the aviator had drinking capability. The M43 was developed into two types:

* Type I for Apache aviators with a notched right eye lens (for compatibility with the AH-64 Integrated Helmet and Display Sighting System [IHADSS] and optical relay tube) with the M171/AIC microphone.

* Type II for non-Apache aviators without the notch and the M133/U dynamic microphone.

The 1990s

The M43A1 (adopted in 1991) was a preplanned product improvement and included an auxiliary motor blower (1 cfm), which could be used in lieu of the standard blower for escape or short-term use. Other user requested items included a second skirt on the hood to improve protection, a standard Army battery for the blower, and a universal microphone adapter for easy switching between the two microphones. The durability of the mask interpupillary distance (IPD) staple was also improved. The IPD adjusted the mask's eye lenses to the user's eyes. The M43A1 even took prescription lenses by using frontserts (like spectacles) mounted on the IPD staple. The M43A2, planned but not adopted, was to use a lightweight blower unit to lessen weight. A few lightweight motor blower units were procured for use in the Gulf War.

While an effective marvel of modem technology, the M43/M43A1 mask system had problems. The M43A1 was briefly considered by the user as an immediate and temporary general-purpose aircrew mask to accelerate the replacement of the M24. Unfortunately, the masks were bulky (the carriers were large and VERY popular for carrying equipment and books), heavy, and the aircraft-mounted blower unit was difficult to remove from the aircraft in an emergency. Attachment and detachment of the M43A1's auxiliary blower unit limited its use in egress and thus minimized its use. Finally, Apache aviators needing prescription lenses had to use contact lenses or have eye surgery because the frontsert interfered with the helmet display unit of the IHADSS. Unfavorable user comments on the heavy aircraft-mounted mask and an unfavorable Department of Defense Inspector General's audit on this piece of equipment led to the development of the M48/M49 masks.

The M48 and M49 masks (adopted in 1996) were essentially M43A1 Type I and Type II masks, respectively, with a lightweight motor blower. The new 4-cfm blower was as powerful as the M43 blower unit but much lighter and pilot-mounted. The aviator wore the blower somewhere on his/her body. Escape from a downed aircraft was theoretically easier with this blower unit than with the M43 blower unit because the escaping aviator did not have to dismount the blower from the aircraft. Also, the 8-hour battery was the same Army standard battery used in the chemical agent monitor. Other government agencies and our allies, including Israel, used the blower. The carrier was still large, but the overall weight was less. The M49 was adopted as an interim standard mask and was not fielded, because the M45 mask was adopted about the same time. While they looked similar, the original M48 had a notched eye lens and a 2-foot-long hose with an elbow connector to attach to the blower. The M49 had two normal eye lenses and a 2-foot-lo ng hose without the elbow connection. As good stewards of taxpayers' money, the Soldier's Biological and Chemical Command (SBCCOM) researched modifying the M49 facepiece to the M48 standard. This modification would save our nation hundreds of thousands of dollars in procuring replacement M48 masks. The M48 and M49 masks, refurbished to the "new" M48 standard, used a new 3-foot hose without the elbow connector, and all M49s had the right eye lens replaced with a notched one.

The M48 Apache mask program, like the earlier M43 series, continued to be controversial. The Apache cockpit area was very cramped. The mask blower was still large, and the question remained, Where did it go? The aviation community initially desired an aircraft-mounted blower unit, which was delivered by the M43. The blower was designed to survive a severe crash and ease operator dismount for emergency egress. Because of difficulties encountered with the aircraft-mounted blower unit, the aviation community opted for an aviator-mounted system, which was adopted as the M48 in 1996.

Concerns about the aviator-mounted blower unit halted the M48 mask fielding close to the initial unit fielding date. There still was a problem with the blower unit interfering with aircraft operations. Advancements in blower technology had not yet produced a low-power consumption unit that was small enough to fit on the aviator without compromising compatibility with aircraft subsystems and survival gear. The project's engineers, working quickly, developed a way to mount the blower on the aircraft in the same location as the M43 blower. In an emergency, the blower could be dismounted in seconds to facilitate the aviator's egress from the aircraft. Minimal modifications were required for the blower unit. The "new" M48 is undergoing testing and has passed every requirement so far. If fully funded, fielding to the full Army Acquisition Objective will occur in 2003.

Until the M48 is fielded, Apache aviators continue to use the M43-series masks. The M43s are reaching the end of their service life. In fact, SBCCOM engineers are visiting units in the Army Reserve, National Guard, and Active Army to check on the masks. Their results show that aviators (like most soldiers) are not conducting preventive maintenance checks and services and correcting or reporting deficiencies. Cracked motor blowers and badly maintained masks abound.

The M45 aircrew protective mask was also adopted in 1996. This mask would replace any M24 masks and M43 Type II masks in the system. The M45 took lessons learned from the M40 mask and was designed using modem plastics. It was--

* Virtually all injection-molded composite and silicone rubber.

* Assembled using modem production methods and ultrasonic welding.

* Designed to fit under the aviator's helmet and allowed the use of night-vision equipment.

* Lightweight and available in extra small, small, medium, and large with replaceable nosecups for a customized fit.

The filter could be attached to the mask either on the cheek or on a hose attached to the belt or body. With front and side voicemitters, the mask can be used for face-to-face and phone communications. To eliminate lens fogging, the design forced the air from the filter over the eye lenses before entering the mouth area to be inhaled. To ensure a good seal, the mask used an in-turned periphery on the mask. While a blower unit could be attached, it was not required because of the excellence of the design. This was the first aviation mask that could be used as a universal general-purpose mask. It is currently in use in the "Land Warrior" program. Because of this adaptability, "aircrew" was dropped from the designation in 1997. This mask is quickly replacing the M24 mask as the standard mask for non-Apache aviators.

The 2000s

Current aviator masks work extremely well, but they are built for the low-level Army aviator. They cannot be attached to the Navy and Air Force oxygen systems and are not fully tested for high-speed flight use. In the continuing interest of standardization, a joint project--the Joint Services Aircrew Mask (JSAM) Program--to design a standard mask for aviators is ongoing. JSAM will provide maximum compatibility and the best protection for all aviators, while easing the Armed Forces' logistical burden. The Army is a full partner in this program. Expect to hear much about this mask in the future.

Conclusion

The aviation protective mask has undergone continuous development. As technology changes, the masks became more effective in protecting the aviator and less burdensome to wear. The original masks provided the requisite protection but were not completely adequate for long-term performance. The current masks represent the latest in military technology. They provide the best possible protection against chemical and biological agents while reducing aviator fatigue. Future masks will provide the best protection for all services and lessen impacts on the supply system.

References

"Aviation Gas Mask Development, Request for Clarification of Military and Technical Characteristics," Office of the Chief, Chemical Warfare Service, 29 June 1943.

"Cancellation of the Aviation Gas Mask as Service Test Type and Cancellation of the Military Requirement Therefore," Item 1621, Chemical Warfare Technical Committee, 13 July 1946.

"Cancellation of the Aviation Gas Mask as Service Test Type and Cancellation of the Military Requirement Therefore," Item 1692, Chemical Warfare Technical Committee, 24 September 1946.

Decker, Richard. (Project Officer), "Test Report Development Test II (PQT-G) of XM33 Protective Mask, Hood, and Combat Spectacles," Systems Test Division, U.S. Army Aviation Development Test Activity, Fort Rucker, Alabama, December 1982.

Edgewood Quarterly Issue 5, March 1995, ATTN: SCBRD-AIC,APG, Maryland 21010-5423.

Edgewood Quarterly Issue 10, January 1997.

"Final Engineering test of Mask, Protective, Helicopter, E75R2, with the E34 Protective Hood" Engineering Test Branch, Test Design and Analysis Office, Tech Operations Directorate, Dugway Proving Ground, Dugway, Utah, August 1960.

"Final Report on Test of Assault Type Gas Mask for Use by Airplane Crew Members," Proof Department, AAF Proving Ground Command, Eglin Field, Florida. 16 December 1943.

http://www.armyavnmuseum.org/history/overview.html, opened 0750 hrs, 28 December 2001.

Letter, CMLPD-CE, DA Office of the Chief Chemical Officer, Washington 25, DC, Item 3312, Subject: Report of Project Nr AVN 1155, Evaluation of Gas Mask for Helicopter Aviators (DA Proj Nr 4-80-12-007-02; RDB Tech Obj CW-46), 23 April 1957.

Memorandum, Edgewood Arsenal, Mechanical Division, Subject: The Gas Mask, 26 March 1927.

"M45 Aircrew Chemical-Biological Mask System," Edgewood Enterprise, January 1997.

"M48/M49 C-B Aircraft Mask" Edgewood Enterprise, May 1997.

"Revised Military Characteristics-for Aviation Gas Mask," Item 1280, Chemical Warfare Technical Committee, 22 March 1945.

Smart, Jeffrey, "History of the Army Protective Mask" Powerpoint Presentation, ATTN: AMSSB-PM-RNN E4465, U.S. Soldiers Biological and Chemical Command, Edgewood, Maryland, October 1999.

TM 3-4240-280-10, Mask, Chemical-Biological, Aircraft, M24, March 1976.

TM 3-4240-312-12 & P, Mask, Chemical-Biological, Aircraft, M43, June 1988.

TM 3-4240-341-10, Mask, Chemical-Biological, M45, May 1998.

Lieutenant Colonel Walk is an Active Reserve chemical officer currently attending the Army War College. He previously served as WMD training officer and executive officer in the G-3, United States Army Reserve Command. Other assignments included chemical officer positions in the 84th Ordnance Battalion and 60th Ordnance Group; acting battalion commander, 1st Battalion 377th Regiment; commander, HHC, 59th Ordnance Brigade; and commander, 184th Chemical Detachment.

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