2


Evolution of Combat Helmets based

2.0 SUMMARY

Combat helmets have evolved considerably over the years. This chapter describes the changes in design and materials, from those used in World War I to today’s Advanced Combat Helmet (ACH). One of the key advances was the development of aramid fibers in the 1960s, which led to today’s Kevlar-based helmets. The Department of Defense (DoD) is continuing to invest in research to improve helmet performance, through better design and materials as well as better manufacturing processes.

2.1 INTRODUCTION

In early usage, soldiers wore equipment made of leather or cloth in an attempt to protect their heads from sword cuts and other blows. When rifled firearms were introduced in the late 1700s, this equipment was found to be inadequate, and its use declined considerably. Over time, the equipment transitioned from providing protection to being an accessory worn for pageantry and unit recognition.

World War I saw a substantial increase in the effectiveness and lethality of artillery, resulting in a new focus on protective equipment, including helmets. The primary threat during this conflict was fragmenting projectiles, and helmets made with steel were introduced for protection in Europe in 1915. Even though stopping a rifle bullet was considered beyond the ability of the helmet materials at the time (due to weight considerations), there were enough benefits to warrant issuing a helmet to all ground troops.

Around this time, the governments in Europe started to invest considerable efforts on research dealing with helmet design, materials, and support systems (such as chin straps and liners). This research resulted, among other advances, in a new grade of metal known as Hadfield steel. Different variations of these steel helmets were used by forces in the United Kingdom and the British Commonwealth during World War I and later. The U.S. military adopted helmets based on Hadfield steel, called the M1 “steel pot,” in 1942. These helmets remained in service until the mid-1980s when they were replaced with helmets manufactured from a nonmetallic material. Small numbers of the M1 helmet are still used today in special missions such as shipboard firefighting.

The beginning of World War II also saw an escalation in the lethality of ballistic threats, resulting in higher fatalities and injuries. The bullets and shrapnel in World War II had greater mass and higher velocities. As was the case with World War I, soldiers initially resisted wearing helmets. They felt that the 3.5-lb helmet was too heavy, and that it limited hearing, vision, and mobility of the wearer. However, the troops quickly accepted the trade-off when they observed the lethality of the munitions on the battlefield and recognized the protection provided by the helmet.

Figure 2-1 illustrates the evolution of U.S. military helmets since World War I. The rest of this chapter discusses the evolution and developments in some detail.

2.2 NEW MATERIALS AND DESIGNS

DuPont invented a new material called aramid fiber in the 1960s. This was a class of strong, heat-resistant synthetic fibers that had many desirable properties. It was eventually marketed under the trade name of Kevlar, and the name would become synonymous with “bulletproof material.” Kevlar represented a breakthrough, enabling a leap ahead in technology of synthetic composite materials. The U.S. government selected Kevlar over other materials that were available at the time, such as nylon, e-glass fiber, and stretched polypropylene. The government was already molding the M1 helmet liner with a similar matched-tool compression molding process, so that the same manufacturing process could be used to make Kevlar helmets.

The Personnel Armor System for Ground Troops (PASGT) was the first helmet to use Kevlar. PASGT refers to both vests and helmets made of Kevlar, and they were used by all military services from the mid-1980s to around the middle of



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2 Evolution of Combat Helmets 2.0  SUMMARY based on Hadfield steel, called the M1 “steel pot,” in 1942. These helmets remained in service until the mid-1980s when Combat helmets have evolved considerably over the they were replaced with helmets manufactured from a non- years. This chapter describes the changes in design and mate- metallic material. Small numbers of the M1 helmet are still rials, from those used in World War I to today’s Advanced used today in special missions such as shipboard firefighting. Combat Helmet (ACH). One of the key advances was the The beginning of World War II also saw an escalation in development of aramid fibers in the 1960s, which led to the lethality of ballistic threats, resulting in higher fatalities today’s Kevlar-based helmets. The Department of Defense and injuries. The bullets and shrapnel in World War II had (DoD) is continuing to invest in research to improve helmet greater mass and higher velocities. As was the case with performance, through better design and materials as well as World War I, soldiers initially resisted wearing helmets. They better manufacturing processes. felt that the 3.5-lb helmet was too heavy, and that it limited hearing, vision, and mobility of the wearer. However, the 2.1  INTRODUCTION troops quickly accepted the trade-off when they observed the lethality of the munitions on the battlefield and recognized In early usage, soldiers wore equipment made of leather the protection provided by the helmet. or cloth in an attempt to protect their heads from sword cuts Figure 2-1 illustrates the evolution of U.S. military hel- and other blows. When rifled firearms were introduced in mets since World War I. The rest of this chapter discusses the late 1700s, this equipment was found to be inadequate, the evolution and developments in some detail. and its use declined considerably. Over time, the equipment transitioned from providing protection to being an accessory worn for pageantry and unit recognition. 2.2  NEW MATERIALS AND DESIGNS World War I saw a substantial increase in the effectiveness DuPont invented a new material called aramid fiber in the and lethality of artillery, resulting in a new focus on protec- 1960s. This was a class of strong, heat-resistant synthetic tive equipment, including helmets. The primary threat during fibers that had many desirable properties. It was eventually this conflict was fragmenting projectiles, and helmets made marketed under the trade name of Kevlar, and the name with steel were introduced for protection in Europe in 1915. would become synonymous with “bulletproof material.” Even though stopping a rifle bullet was considered beyond Kevlar represented a breakthrough, enabling a leap ahead in the ability of the helmet materials at the time (due to weight technology of synthetic composite materials. The U.S. gov- considerations), there were enough benefits to warrant issu- ernment selected Kevlar over other materials that were avail- ing a helmet to all ground troops. able at the time, such as nylon, e-glass fiber, and stretched Around this time, the governments in Europe started to polypropylene. The government was already molding the invest considerable efforts on research dealing with helmet M1 helmet liner with a similar matched-tool compression design, materials, and support systems (such as chin straps molding process, so that the same manufacturing process and liners). This research resulted, among other advances, could be used to make Kevlar helmets. in a new grade of metal known as Hadfield steel. Different The Personnel Armor System for Ground Troops (PASGT) variations of these steel helmets were used by forces in the was the first helmet to use Kevlar. PASGT refers to both vests United Kingdom and the British Commonwealth during and helmets made of Kevlar, and they were used by all mili- World War I and later. The U.S. military adopted helmets tary services from the mid-1980s to around the middle of 11

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12 REVIEW OF DEPARTMENT OF DEFENSE TEST PROTOCOLS FOR COMBAT HELMETS FIGURE 2-1 Evolution of helmets from World War I to present. SOURCE: Walsh et al. (2012). the last decade. These helmets are still being used by some manufacture of thermoplastic-based fibers and matrices for services but will be replaced in the future. affordable soldier protection systems. The programs focused Figure 2-1 fixed image The U.S. Special Operations Command designed and on developing new technologies, tooling, and hybridization developed the Modular Integrated Communications Helmet techniques to enable commercially available and emerging (MICH) as a replacement for PASGT. MICH had several grades of thermoplastic ballistic composite materials to be changes, including improved Kevlar aramid-fiber reinforce- formed into complex helmet shapes. There was participation ment, leading to better protection. They also allowed better from the Marine Corps, U.S. Special Operations Command, fit and integration of communication headsets. MICH was and the industrial sector. These efforts enabled the develop- adopted by the U.S. Army in 2002 as its basic helmet and ment of the Future Assault Shell Technology (FAST) hel- renamed the Advanced Combat Helmet. The Marine Corps met, the Maritime helmet, and, ultimately, the U.S. Marine decided to use a design profile that was similar to the PASGT Corps Enhanced Combat Helmet (ECH). The FAST helmet and designated it the Light Weight Helmet (LWH). is significant for its early use of UHMWPE material and its There were also developments in helmet retention sys- novel design. tems. The M1 “steel pot” used a nylon cord suspension sys- To improve ballistic protection, the Army has initiated tem, sweatband, and chinstrap, and the PASGT helmet and several developmental programs over the last decade. These its variants also used similar retention systems. The MICH, include the Scorpion, Objective Force Warrior, and Future ACH, and LWH helmets switched to a multi-pad and four- Force Warrior programs. The goal of the Scorpion program point retention system (Figure 2-2) that had better impact was to improve protection and performance through an inte- protection while providing increased comfort. grated system. It tried to address the continuing problem of The next major advance in helmet technology resulted protection while also providing the soldier with capability, from a combination of advances in materials and manufac- such as communications, hearing protection, and displays, turing processes. A new generation of ultra-high-molecular- needed in an evolving battlefield environment. The pro- weight polyethylene fibers (UHMWPE) was developed gram also explored the use of materials with better ballistic in industry. In parallel, the government funded efforts to performance and processing concepts to deliver increased address technology gaps that had previously precluded structural performance. In addition, the program examined how to provide more options in helmet shaping, compat-

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EVOLUTION OF COMBAT HELMETS 13 FIGURE 2-2 Helmet multi-pad and four-point retention systems. SOURCE: PEO Soldier, U.S. Army. ibility, and ergonomics as wellFigure 2-2, fixed image as device and accoutrement awareness in all environmental and obscurant conditions integration. These early efforts would ultimately result in an without sacrificing mobility and agility. entirely new generation of helmet technologies, designs, and Unlike past considerations for fielded helmets, the HEaDS manufacturing processes. UP program also explicitly acknowledges that the helmet is no longer simply a device to prevent injury from fragments and blunt impact. It recognizes that the helmet has become 2.3  RECENT DEVELOPMENTS AND DIRECTIONS a platform to provide the soldier with new capabilities to In 2009, the U.S. government launched the “Helmet enhance their survivability. The consequence is further Electronics and Display System–Upgradeable Protection” device integration and modularization of accoutrements in (HEaDS-UP) program, involving multiple organizations. or attached to the helmet. It might mean even more ballistic As of 2012, it was the largest head-protection research and protection from small arms threats and maxillofacial (man- development project within the Army. It leverages mul- dible) systems that can be rapidly donned or doffed. But the tiple efforts—in the areas of ballistic materials (transparent advances are limited by the total amount of weight a soldier and non-transparent), high-resolution miniature displays, is able to carry for an extended period of time. and sensors—to design a modular-integrated headgear Continued improvement in materials is also leading to system that takes into account the relevant ergonomics advances in helmet performance. For example, ECH delivers considerations. much better protection against fragments compared to ACH, The HEaDS UP program is designed to include participa- due to a shift to unidirectional UHMWPE fiber in a ther- tion from a wide spectrum of Army organizations as well as moplastic matrix. The shift was also enabled by a new gen- other services and government agencies. The goal of the pro- eration of preforms and manufacturing methods appropriate gram is to provide two different and independently developed for UHMWPE. While other promising materials have been concepts of an integrated headgear system and packages of identified (e.g., copolymers, graphene, and high-tenacity design options as well as guidelines based on manufacturing UHMWPE), dramatic weight reduction without a significant best practices, lessons learned, and technology maturation. loss in ballistic performance has been elusive. The resulting insight will be used to develop an integrated Another factor in helmet protection is the way the con- head, face, and neck protection headgear system that incor- stituent materials are assembled. Previous research results porates modular, upgradeable protection. suggest that, in unidirectional UHMWPE panels, varying The soldier-relevant goals are twofold: (1) reduced weight fiber orientation and fiber architecture can provide better for equivalent protection and small increased weight for sig- balance between resistance-to-penetration and deformation nificantly increased capabilities; and (2) increased situational

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14 REVIEW OF DEPARTMENT OF DEFENSE TEST PROTOCOLS FOR COMBAT HELMETS mitigation. Vargas-Gonzalez et al. (2011) have explored this DoD has undertaken extensive efforts to improve combat issue for panels that had more architectural complexity. helmet designs. The design goal is to reduce injuries and New materials are also under evaluation for mitigating injury severity, while achieving operational needs. However, the effect of impacts to the head. Both recoverable and non- the goal of this report is to evaluate test protocols. In the recoverable energy-absorbing materials are being considered following chapters, the extent to which the above goal—of for use as helmet pads. Concepts for decoupling the helmet reducing injuries and injury severity—is achieved by the test into a ballistic and impact shell (and using energy-absorbing programs is discussed. materials between shells) are also being explored. Novel manufacturing equipment and methodologies also 2.4  REFERENCES have a role to play in improving performance. The first gen- eration Helmet Preform Assembly Machine is an example of Vargas-Gonzalez, L.R., S.M. Walsh, and J.C. Gurganus. 2011. Examin- ing the Relationship Between Ballistic and Structural Properties of a process that exploited the ability of thermoplastic compos- Lightweight Thermoplastic Unidirectional Composite Laminates. ARL- ites to be locally consolidated, leading to a rapid, automated RP-0329. Army Research Laboratory, Aberdeen Proving Ground, Md. method of stabilizing and building up helmet preforms. The Walsh, S.M., L.R. Vargas-Gonzalez, B.R. Scott, and D. Lee. 2012. Develop- underlying lesson is that processing should also be explicitly ing an Integrated Rationale for Future Head Protection in Materials and considered as an asset in pursuit of incremental performance Design. U.S. Army Research Laboratory, Aberdeen Proving Ground, Md. gains in head protection materials and systems.