By: William Greer, Jr.


U.S. Marine Corps Photo

Today, the Air Force continues to improve CBRN survivability across its MCSs as well as work with the joint CBRN defense community on solutions to modernize and enhance total capability. This article briefly discusses CBRN survivability in the Air Force prior to PL 108-375 and DoDI 3150.09, the Air Force’s CBRN survivability strategy for existing and new MCS, and several Air Force initiatives to bolster CBR contamination survivability and enhance mission capability as CBRN survivability evolves to meet changing CBRN threat environments.

MCS CBR contamination survivability involves a mix of three elements: hardness, human compatibility, and decontamination. Together, these elements constitute the parameters that define the criteria for quantifying a system’s CBR contamination survivability capability. Finding the right balance to make a system suitably survivable, while achieving its required capability, requires assessing the system against CBRN threats in the context of its mission(s) and how well these three elements come together for the system to achieve a given contamination survivability capability. For both existing and new MCSs, CBRN survivability needs and the means to achieve a desired degree of CBRN survivability will change as threats evolve and CBRN survivability technologies improve. If an identified threat can degrade mission capability, or a system can otherwise benefit from improved CBRN survivability, further assessment will be needed to weigh the cost and benefit to enhance its survivability.

For example, any system can be absolutely CBRN survivable against all possible threats, well beyond what may ever manifest over the life of that system. However, the costs of added CBRN survivability—including impact on the acquisition life cycle; degradation of mission capability; cost to maintain; and impact on daily operability, maintainability, and reliability—must be weighed against the risks of operational effectiveness degradation or loss without improving one or more elements to enhance CBRN survivability capability. CBRN survivability is addressed in an ongoing process of MCS improvements to strengthen CBRN survivability capabilities over a system’s life cycle along with looking to enhance agile combat support CBRN survivability capability within the Air Force.

Air Force and DoD CBRN survivability policies promote developing the right mix of CBRN survivability attributes in an MCS beginning at the earliest design phases, where a system developer can work to balance CBRN threats over the system service life and determine how each CBRN survivability element may factor into the operational design. The Air Force portfolio of existing MCSs includes numerous legacy systems developed years before enactment of PL 108-375, and developers did not always address CBRN survivability (as defined by DoDI 3150.09) during the acquisition phase. Attempting to determine what CBRN survivability was incorporated into legacy MCSs, while also ensuring CBRN survivability was addressed during the procurement of new systems, was an early task the Air Force set out to accomplish with the publication of AFI 10-2607. The Air Force is currently working to evolve both legacy and new MCSs so that Air Force-wide investments in MCS CBRN survivability capability continue to serve as an effective CBRN deterrent, as articulated in the current version of DoDI 3150.09.


Since World War I and the introduction of chemical weapons in modern warfare, each Service’s approach for setting CBRN requirements was based on Service-specific capability needs in terms of developing required weapon system contamination survivability capabilities. This fact resulted in a mix of capabilities driven by Service-specific views on what was necessary to fight battles and win wars. Accordingly, the Army emphasis for years after World War I was on chemical warfare threats to land forces while the Navy focused on blue water threats to battle groups.

After World War II, the CBRN landscape changed as the United States and Soviet Union took on the roles of opposing superpowers, and the driving threat was the growth of nuclear weapons and intercontinental delivery systems. During this period, the Services, including the newly formed U.S. Air Force, worked to reshape themselves to counter the dominant CBRN threat: nuclear attack. This reshaping included developing new weapon systems able to survive long enough to deliver nuclear weapons to targets across the globe. During this time, nuclear effects and radioactive fallout, rather than chemical and biological (CB) threats, drove Air Force survivability.

As the Cold War continued, both the United States and the Soviet Union developed large inventories of nuclear weapons and amassed CB capabilities as part of the mix of offensive weaponry each side had stockpiled in the event the Cold War turned hot. Along with offensive capability being developed and procured, defensive capabilities were developed to make MCSs more CBRN survivable, although a good deal of this effort focused on items such as protective ensembles for personnel vs. altering or incorporating integrated CBR defense capabilities into MCS designs.

CBRN survivability during this period was treated as capability needed to defeat a Soviet/Warsaw Pact onslaught ending in total defeat of one side or the other; reconstituting post-global-war MCSs was not a priority. This was a logical approach, as MCSs employed materials that were not significantly degraded by sustained CBR exposure over the course of days or weeks (they were viewed as inherently hardened for CBR exposures) and the focus rested instead on protecting personnel over similar periods of days or weeks. While MCS decontamination was an integral part of training, it typically was focused on the immediate hazard and involved such practices as scrubbing exposed surfaces with hot soapy water that were intended to reduce hazards to levels allowing operations to continue (vs. restoring systems to unrestricted use among the general population).

During this time, CBRN requirements for various systems varied significantly as requirements and CBRN survivability options continued to evolve. Pre-DoDI 3150.09 baselines for systems CBRN survivability are still a factor in today’s survivability because many legacy MCS designs were influenced by Service-specific contamination survivability assumptions. While their missions evolved along with the CBRN threat, their designs reflect, to some degree, their baseline CBRN survivability capability.

For example, for several decades after the U.S. Air Force was stood up, the primary CBRN threat was driven by the Cold War. As mentioned, nuclear and (potentially) radiological fallout drove CBRN (then often referred to as nuclear, biological, and chemical [NBC]) survivability, where either CB threats did not pose a major unique threat for Air Force weapon systems under original deployment scenarios or only one or two survivability elements were addressed in acquisition requirements and testing. Instead, systems were developed with inherently CBRN survivable materials mitigating impact, or it was often assumed that significant CBR contamination would lead to the MCS becoming a battlefield loss (equipment destroyed). As a result, some specific traits such as material compatibility were not necessarily tested in detail or verified in field trials.

Several techniques were developed to remove CBR, and while various methods were explored, procedures called out over the years in the various service manuals were “hot soapy water” and weathering. Both approaches were tested in recent years and found to not always clean complex weapon systems to the cleanliness levels expected today.

The post-World War II focus carried well into the 1990s, impacting how MCS developers addressed full CBRN survivability. Then emphasis was on two key CBRN survivability attributes: hardness and compatibility. Both were formulated to ensure MCSs could operate and execute missions through World War II-scale scenarios. However, when it came to restoring or recovering weapon systems, historical literature; field manuals (FMs); and tactics, techniques, and procedures (TTPs) for decontamination did not provide guidance to clear systems, suggesting the overall assumption was that contaminated systems would be abandoned or destroyed as no criteria were defined to fully restore weapon systems to unrestricted operations.

The 1993 version of FM 3-5, for example, speaks to immediate, operational, and thorough aircraft decontamination but emphasized avoidance as many decontamination methods were highly corrosive [3]. Clearance-level decontamination for aircraft was not addressed in the 1993 FM 3-5 version.

With the end of the Cold War, many MCSs were driven by a post-Soviet worldview, where weapons of mass destruction (WMD) were treated more as an isolated regional threat and not all systems required robust CBRN survivability capabilities. However, with the end of the Soviet Union and global initiatives to reduce CBRN weapon stockpiles worldwide, MCS CBRN survivability began to lose focus in the 1990s; and within a decade, concerns arose. These concerns were documented by the Government Accountability Office (GAO) in May 2003 (in GAO-03-325C) and again in April 2006 (in GAO-06-592) [4, 5]. Congress and the Bush Administration also focused on this concern under the October 2004 Ronald Reagan National Defense Act. These reports and legislation led to the DoD issuing DoDI 3150.09 in 2008.


Air Force MCSs come in many forms with capabilities to project force across a range of operational environments. CBRN threats that each MCS faces now and into the foreseeable future vary dramatically from system to system. Thus, assessing each system’s contamination survivability capability must be framed and weighed against a mission-focused threat to ensure each has a level of survivability in line with a particular weapon system’s mission. Within AFI 10-2607, processes are set forth to address CBRN survivability, the implementation of which is discussed in the following text.

AFPD 10-26 implements DoDI 3150.09 and (through AFI 10-2607) sets in motion initiatives to strengthen contamination survivability for both legacy and new MCSs [6]. Among the MCSs in the Air Force inventory, aircraft are the systems most likely to face major CBR threats. As such, aircraft contamination survivability is at the forefront of CBRN survivability work as the Air Force engages with the joint CB defense (CBD) community to develop new and innovative solutions to enhance MCS contamination survivability.

Table 1 lists some top-level attributes developers consider as new system designs mature. Realizing these types of attributes in aircraft designs requires an understanding of how the threat manifests; of existing capabilities employed operationally; of the ongoing progression of CBRN survivability initiatives; and, in turn, of developing approaches to improve the system’s capability.

Implementation also calls for employing requirements analyses and systems engineering principles to all phases of the acquisition life-cycle process, as well as filling data gaps present in our understanding of contamination survivability and developing more robust operational capabilities.

CBRN is a threat collectively made up of quite divergent and unique threats. For much of Air Force MCS contamination survivability, the focus is on CBR. Nuclear survivability is concerned with prompt weapon effects associated with the immediate nuclear blast whereas CBR centers on the contamination resulting from CBR weapons, including radiological dispersal devices and low-level nuclear explosions.

Developing MCS solutions for chemical vs. radiological vs. biological contamination survivability does not lend itself to a one-size-fits-all approach. Instead, each must be considered independently (see probable aircraft exposure examples in Table 2). CBRN survivability requirements should be tailored so each system’s incorporated contamination survivability is balanced to avoid excess requirements driving a design where CBRN survivability may come at the expense of other important performance requirements.

Table 1 Sample Contamination Survivability Considerations for Aircraft Systems


Table 2 Typical Aircraft CBR Exposure Routes

For aircraft, where designers push materials to their limits to get the most out of every ounce of mass added to an airframe, chemical challenge is often the focus of developers for CBR vulnerability assessments. Exposure and its impact on materials must be understood in detail, as even a small degradation of material performance can have a significant impact. This understanding requires detailed studies, as CBR threats vary by agent and can manifest as both an immediate and long-term hazard and present as either a liquid or a vapor challenge. Biological and radiological threats generally present themselves as particles and have discrete properties that do not normally pose an immediate material hazard from an MCS vulnerability standpoint but may be problematic from an overall contamination survivability perspective.

For example, biological weapons typically do not show up in vulnerability studies of MCS hardness, as biological weapon organisms are selected because they are effective against people but have no history of quickly damaging materials normally employed in Air Force MCSs. However, when looking at all aspects of contamination survivability, focusing on both hardness against the threat and effective decontamination solutions presents a major contamination survivability challenge. Decontamination of anthrax spores, the most resilient form of Bacillus anthracis, is extremely difficult with aircraft. Many standard approaches employing sanitizing solutions such as chlorine can cause irreparable damage to some sensitive components in many Air Force MCSs.

As discussed, Air Force systems historically focused on biological threats as a “survivability afterthought” as they most generally did not pose a risk of mission failure while fighting a war. The question of recovering and returning aircraft to unrestricted operation was ignored; it was considered too difficult to warrant dedicating resources or would become someone else’s problem after the fighting ended.


CBR operational impact is MCS-specific, and understanding how each CBR threat can impact a given MCS enables incorporation of effective CBR contamination survivability into the MCS design process. As new system acquisitions take place, the CBRN survivability threat assessment is the analytic framework enabling the system developer to define CBRN survivability performance requirements the MCS should meet. Incorporating CBRN survivability into the systems engineering process allows designers to factor in various CBRN survivability strategies to meet defined performance requirements as the system design advances.

There are no prescriptive solutions to achieve CBRN survivability for MCSs. It is important to remember that for each Service, CBRN survivability requirements are driven by Service requirements and, within a Service, by mission needs. The Air Force has a variety of aircraft, both manned and unmanned, covering missions ranging from the nuclear enterprise and cyber security to acquisition, deployment, and operation of MCSs to support a multitude of users across the joint community.

Readers will recognize that CBRN survivability requirements for a cyber MCS will likely not be the same or employ the same solutions as those for space-based systems. Air Force CBR contamination survivability assessments reflect this reality; and as Air Force acquisition organizations implement DoDI 3150.09 and AFI 10-2607 requirements, they are working to balance cost, performance, and risk to get the best value. For systems at the greatest risk of CBR exposure, designers are employing systems engineering processes to develop end-to-end contamination survivability approaches.

As discussed previously, fundamental differences between threats call for assessments based on each threat’s unique properties. Chemical threats present as vapor or liquid while biological and radiological threats generally present as particles. Whereas radiological particles create an ionizing radiation hazard, biological threats generally involve infection. The assessment of each CBR threat should draw on expertise that spans highly divergent fields of study, such as chemistry, physics, and biology. As developers delve deeper into the hazard impacts, other specialties, such as materials sciences, health physics, and toxicology may be required to understand how sensitive materials behave and how mitigation mechanisms in a design can limit personnel exposure during dirty operations.

For aircraft, where designers seek to maximize system performance, CBRN survivability approaches that add weight or degrade performance parameters will often be targeted in trade studies, potentially leading to reduced CBRN survivability capability and increased operational risk. Addressing CBRN survivability in the design often involves finding ways to harden the system and minimize contamination during exposure. Hardening the system though material selection is a crucial step in design resiliency against the threat, but that selection process should also factor in decontamination, as a treatment selected as an afterthought may be ineffective or be more destructive than the threat exposure in terms of potential system damage.

For MCSs such as aircraft, CBRN survivability is advancing on Air Force programs as developers formulate innovative approaches to satisfy system CBR contamination survivability requirements. A major step the Air Force has taken toward advancing comprehensive CBR contamination survivability is in system-level CB decontamination. Over the past 8 years, research and development has moved forward on system-level CB decontamination using only heat and controlled humidity, which are shown to inactivate biological threats and induce controlled accelerated weathering of residual chemical hazards (desorption).

Using the same underlining technology, two distinctly different decontamination mechanisms have been demonstrated both in the lab and in operationally representative field tests and demonstrations. As a result of this work and the effectiveness demonstrated to date, several new Air Force aircraft programs are adopting this technology by adding given parameters to the aircraft’s performance requirements for CB decontamination. Air Force policy requiring developers to address CBR contamination survivability and, in particular, decontamination is taking hold in the acquisition offices’ systems engineering processes. These acquisition programs are now working on the best approaches for implementing new decontamination methods within their designs when possible.

In turn, as this new approach gains momentum, joint agencies responsible for advancing the science, technology, and development of decontamination systems are investing to bring system-level operational decontamination capabilities to the Services. The Air Force is working closely with the Joint Program Executive Office for CB Defense (JPEO-CBD), the Joint Program Manager – Protection (JPM-P), and operational commands to field an operational capability, the Joint Biological Agent Decontamination System (JBADS), in the next several years.

For legacy systems, strengthening CBRN survivability is a challenge as the enhancements must be handled retroactively and conform to established design parameters. Fortunately, some mitigation actions are achievable as part of the sustainment process. For chemical threats, work on new, more effective coatings is advancing, and these coatings may also offer improved weapon system performance properties beyond reducing chemical agent absorption and contamination migration. Coatings that provide improved chemical warfare agent protection also tend to be more resistant to a wide range of chemicals that can affect a system over time, such as heavy air pollution, tropical humidity, salty air, and other contributors to long-term corrosion. In the case of aircraft, these coatings can also be beneficial by enhancing de-icing and reducing drag. These types of non-CBRN survivability cost benefits go a long way toward driving adoption of CBRN survivability enhancements in legacy systems as well as in new acquisitions as part of the overall systems engineering process.

In addition to approaches to harden the MCS through relatively simple changes, such as new coatings, joint research by the JPM-P program office and the Air Force Research laboratory (AFRL) (including lab and field tests) are showing promising results in the field of chemical decontamination. This work employs a hot air decontamination process that was identified early in the F-35 system design process. The approach works within the boundary of Air Force long-term storage temperature limits, a design envelop the Air Force employed for many legacy systems.

This long-term storage temperature limit was originally part of the F-35 airframe design, and testing to date shows promise in terms of controlled heat being safe to use on F-35 and meeting specified decontamination targets.

On the biological front, a similar method, JBADS, employs biothermal decontamination where the aircraft is heated (within the aircraft’s long-term storage design limit), and controlled relative humidity creates a decontamination environment throughout the aircraft (Figure 1). JBADS was demonstrated in late 2014 during an Operational Utility Assessment (OUA) on a C-130H aircraft. Several tests confirmed JBADS effectively inactivated robust spore-forming organisms, such as Bacillus thuringiensis var. kurstaki (Btk), a hardy endospore that is as difficult to kill as its cousin Bacillus anthracis. Btk was selected as a simulant as it is environmentally safe and available commercially in the organic pest control section of many home and garden supply stores. A JBADS-based CB decontamination system was also used for the F-35 CB Live Fire tests beginning in late 2016 to verify the aircraft’s biological decontamination capability.

The C-130H and the F-35, a legacy system and a new system, were treated to confirm effective biological decontamination employing the JBADS processes and confirm that each aircraft tested remained flyable after the treatment. While the C-130 and the first F-35 test aircraft were both removed from flight status prior to testing, maintenance inspections confirmed both systems were flyable. A second F-35 completed testing in March 2017 and returned to its home base after testing to verify the aircraft met its decontamination requirements. Results of the F-35 tests will be published later in 2017.

In addition to demonstrating decontamination, the JBADS approach also is moving beyond biological weapons and finding value in the Air Force as a novel tool to kill mold and mildew in aircraft. In the last 2 years, the JBADS processes were employed to treat various molds and mildews discovered under floor bays of an operational C-5B, in the forward and tail fuselage sections of an operational C-130 (see Figure 2), and most recently in a forward fuselage of an F-35. The treatments were effective, and the Air Force saved several million dollars over established hand-cleaning methods.

The dual-use approach leveraging contamination survivability technology was not originally planned, but JBADS developers—such as the AeroClave Corporation, which conducted the JBADS trials in 2014—found the opportunity to effectively employ JBADS technology to address non- WMD needs and show (through operational experience) that the processes are safe and effective for legacy systems, with no changes required to the aircraft.

These are a few examples of work underway by the Air Force and JPM-P to develop new decontamination capabilities that, while driven by limitations of sensitive materials and equipment on

Figure 1 C-130 JBADS Decontamination Enclosure Being Set Up for a 2014 OUA


Figure 2 Mold in the Galley (top) and Avionics (center) of a C-130 and the C-130 Interior Mold Treatment Underway (bottom)

aircraft, can also be employed by other Services, federal agencies, and organizations interested in decontamination where these processes can meet biological mitigation/remediation needs. JBADS does not address some Service rapid decontamination requirements, as the processes take several days and are intended to support decontamination needs of MCSs with sensitive materials and equipment. Users with suitably hard equipment or weapon systems may choose other approaches (designed to decontaminate in minutes or hours) as a preferred solution when speed is a priority. Air Force leaders agree that removing an aircraft from operations after hostilities subside for a few days or weeks to restore it to normal unrestricted operations is much preferred to rapid decontamination treatments that may permanently degrade or risk loss of each contaminated aircraft.


Along with implementing policy, assessing current capabilities, developing more robust CBRN survivability requirements, and embedding CBRN survivability into the systems engineering process for new systems (and for upgrading legacy systems), the Air Force is working with both the JPEO-CBD community and the Defense Threat Reduction Agency (DTRA) to advance CBRN survivability technologies. Over the past 2 decades, the Air Force has undertaken several initiatives to improve CBRN survivability, spanning development of innovative TTPs to enhance operations in dirty environments, and has invested in CBRN survivability across MCSs.

Studies have included research on chemical agent fate to explore alternate TTPs to reduce hazard exposure. These studies, which have led to implementing Split Mission-Oriented Protective Posture (Split MOPP) to facilitate restoring airbase operations, have been incorporated in Air Force Manual (AFMAN) 10-2602. However, while Split MOPP has helped to reduce the burden of airman continually wearing MOPP gear on a base with dirty zones, it has not prevented hazard exposure and has meant that equipment, including MCSs exposed to chemical agents, needed to be decontaminated.

Studies performed by DTRA and the Air Force explored several approaches to decontaminate systems, and from that work, AFRL embarked on developing system-level decontamination, employing heated air to desorb and induce accelerated weathering to reduce hazards without harming aircraft (as discussed previously). In conjunction with tackling chemical decontamination with hot air, AFRL also explored other biological decontamination potential approaches. Based on those studies, AFRL focused research on heated air combined with controlled humidity to achieve biological decontamination.

This research has made major strides in a few short years as AFRL led the JBADS Joint Capability Technology Demonstration (JCTD), which helped advance system-level biological decontamination to a Technology Readiness Level 7 through tests performed using a C-130H. With the success of the JBADS JCTD, further testing was conducted, and the JBADS process was selected for the F-35’s biological decontamination. A second prototype CB decontamination system was then developed by JPM-P for the F-35 Live Fire Test, combining these two methods.

Related Air Force CBRN survivability research initiatives are also showing promise. AFRL research has produced a new coating dubbed “Diamondback” that shows some promise in resisting chemical absorption, and it is undergoing long-term environmental tests as a CBR contamination survivability coating to mitigate contamination and help with de-icing and in-flight drag. Other studies over the past decade have centered on more foundational research evaluating the properties of materials exposed to chemical hazards as well as some decontamination systems. This research explored and quantified material properties and compatibility for numerous MCS materials to identify degradation due to agent exposure as well as degradation risks possible from some decontamination solutions. This research is ongoing, and as materials are assessed, AFRL is publishing results to materials databases to promulgate what is learned so system developers can access and be informed on material effects and, in turn, improve their system’s CBR hardness.

This year also saw AFRL along with Navy researchers kick off studies to quantify the effects of ocular exposure to chemical agents. This research will help to answer questions about the exposure risks to aircrew and the ability of aircrews and other warfighters to perform mission-critical operations if low-level exposure manifests as ocular meiosis, which can, for example, degrade aircrew performance.

These initiatives have spanned both material and nonmaterial solutions. This work will help to advance CBRN survivability for MCSs as the Air Force looks at ways to limit exposure, operate more effectively when MCS is contaminated, and develop/adopt technologies to mitigate hazards. These advances may allow the Services to balance material and nonmaterial options and operate dirty, knowing their MCS capabilities are not being significantly degraded. And when the time comes, the Services can reconstitute the forces and warfighting assets and employ effective decontamination methods to restore MCS to full operations.


Since the signing of PL 108-375 and its implementation through DoDI 3150.09 and AFI 10-2607, the law’s impact continues to reverberate within the Air Force. Surveys were done to assess the state of MCSs across the Air Force, and steps were taken to bring a balanced contamination survivability capability to MCSs and strengthen contamination survivability capability through multiple avenues. These avenues have included evolving concepts of operations (CONOPs) and TTPs, embedding contamination survivability in the systems engineering process of systems identified to be CB survivable, developing technology solutions, and engaging with the joint CB defense community. Furthermore, studies have identified opportunities and needs to help the Air Force invest and grow CBRN survivability capability through a mix of material and nonmaterial options.

Implementation is ongoing, and a good deal is being accomplished today. Within the Air Force CBRN community, however, there is still much to do to embed the right mix of CBR contamination survivability capabilities into MCSs to meet mission needs. This accomplishment will not happen overnight, but those practitioners working in these issues are seeing positive trends as they strive to strengthen the Air Force’s ability to ensure MCSs survive any known and future CBRN threats as the Air Force carries out its global mission.


Mr. William Greer leads the AFRL Human Performance Wing’s Aircraft CBRN Survivability team and advises various Air Force organizations on CBRN contamination survivability and related topics. With more than 23 of active duty Air Force service, Mr. Greer has led numerous CBRN Air Force modeling, simulation, and analysis projects; CB operational impact studies; and CBRN research and development projects. He was also selected to lead the Department of Energy’s nuclear and radiological consequence management programs. Currently, he works with the Air Force’s aircraft development program offices and conducts developmental research of system-level aircraft decontamination capabilities to address CBR contamination survivability on legacy and new aircraft systems. Mr. Greer holds a B.S. in mechanical engineering from Syracuse University and an M.B.A. from Chapman University.


References [1] U.S. Secretary of Defense for Acquisition, Technology, and Logistics. “The Chemical, Biological, Radiological, and Nuclear (CBRN) Survivability Policy.” DoDI 3150.09, September 2008. [2] U.S. Secretary of the Air Force. “Air Force Chemical, Biological, Radiological, and Nuclear Survivability.” AFI 10-2607, April 2016. [3] Headquarters, Department of the Army, and Commandant, U.S. Marine Corps. “NBC Decontamination.” FM 3-5 and FMFM 11-10 17, U.S. G.P.O. 1993-728-027:80075, November 1993. [4] Government Accountability Office. “Chemical and Biological Defense: Sustained Leadership Attention Needed to Resolve Operational and System Survivability Concerns.” GAO-03-325C, 30 May 2003. [5] Government Accountability Office. “Chemical and Biological Defense: DOD Needs Consistent Policies and Clear Processes to Address the Survivability of Weapon Systems Against Chemical and Biological Threats.” GAO-06-592, April 2006. [6] U.S. Secretary of the Air Force. “Countering Weapons of Mass Destruction Enterprise.” AFPD 10-26, June 2015.