Experts say developing states could counter U.S. missile defense. History shows it’s more complicated.
Ballistic missile defense (BMD) has remained a contentious topic within the U.S. security policy community. To its proponents, its benefits are manifold, reassuring allies, providing “additional time and options for national leaders” during crisis, and “diminish[ing] the perceived value of missiles as tools of coercion. To critics, missile defense fails to deliver on its technical and strategic promises. Notwithstanding its mixed test results and ballooning costs, these voices argue that BMD could undermine deterrence and provoke adversaries into assuming increasingly dangerous nuclear postures. 
The United States’ adversaries have not waited for this sixty-year debate to conclude. Effective or not, strategic competitors have consistently and openly expressed anxiety over U.S. missile defense. In response to U.S. BMD deployments to South Korea in 2016, for example, China imposed punishing sanctions on South Korean businesses.And since the Cold War, U.S. missile defense programs — from the ill-fated Sentinel/Safeguard to today’s Extended Phased Adaptive Architecture (EPAA) — have caused equal consternation in Moscow, eliciting condemnation and precipitating arms limitation talks.
In short, the promise of missile defense creates strong incentives for states to develop countermeasures. These approaches can range from operational changes — like striking defensive assets early in a conflict or utilizing depressed trajectories — to technical ones: creating devices to confuse or overwhelm BMD systems. This paper will focus on technical countermeasures: devices installed on ballistic missiles to enhance their ability to penetrate missile defense. Also termed “penetration aids” (penaids), these systems can include radar-reflecting chaff, electronic jammers, decoy warheads, and maneuverable or stealthy reentry vehicles.
Most major powers — including China, the United Kingdom, and the United States — have intensively pursued such countermeasures in the past. Today, these states have continued to demonstrate new capabilities, while intelligence reports suggest that emerging missile powers like North Korea have already acquired rudimentary systems. States are clearly interested in countermeasures, and technical analyses by Sessler, Postol, and others suggest that basic penetration aids are relatively simple to develop.  Yet few discuss the how states have historically acquired countermeasures. What shape do these development projects take?
Despite the considerable interest in missile defense policy, detailed accounts of major countermeasures programmes remain sparse. Aside from several major works on Chevaline, a 1970s-era British penetration aid, few have attempted a comprehensive historical description of U.S., Soviet, Chinese, or French penetration aids programs. The absence of detailed case studies is not surprising. In regimes where weapons procurement programmes were 1) poorly documented or 2) not subject to political scrutiny, it may be difficult or impossible to piece together a detailed narrative in the open source. Moreover, the very nature of countermeasures — as a technical means to reduce confidence in missile defense — can preclude detailed disclosure of these systems even in open societies.
But historical case studies are still possible to construct. Scholars have not yet explored the dearth of declassified records on U.S. countermeasures efforts during the Cold War. In addition, U.S. decisionmakers often openly discussed penetration aids through the mid-1960s. In the tradition of other historical evaluations of the U.S. strategic weapons program, this article develops a case study of U.S. countermeasures development from 1957 through the present. After crafting a general timeline of relevant programs, this paper synthesizes three themes: that the countermeasures effort was 1) hampered by technical difficulties, 2) driven by a mix of strategic and bureaucratic imperatives, and 3) dwarfed in importance by the growing push for Multiple Independently-targeted Reentry Vehicles (MIRVs). The paper then ends with a general discussion of the case’s comparative utility and its ramifications for the missile defense discourse.
U.S. interest in countermeasures began abruptly as the Soviet Union began flight testing antiballistic missiles (ABM) in 1957. Alarmed by reports of Soviet BMD, the United States conducted feasibility studies of penaids later that year. The studies — commissioned independently by the Gaither Committee, the Department of Defense’s Reentry Body Identification Group (RBIG), and the President’s Science Advisory Committee (PSAC) — were first to hypothesize the penetration modes investigated in future programs and recommended initiating a program of record on penetration aids.
By the early 1960s, countermeasures development became a department-wide priority. In 1962, the Air Force, Navy, and Army established the Advanced Ballistic Re-Entry Systems (ABRES) program, centralizing research and development under Air Force management. Over growing concerns about Soviet capabilities, ABRES and the services funded research on over 24 distinct approaches, investigating chaff, reentry decoys, electronic countermeasures, radar cross-section reduction, plasma wake manipulation, and maneuvering warheads by the mid-1960s. Consequently, Air Force spending on penetration aids quadrupled in size, ballooning from $35.5 million (unadjusted) to $155 million in 1964.
U.S. investment in ABRES reached a peak by the mid-1960s. Under ABRES and TRADEX, a BMD testing program, researchers flight tested several types of enveloping balloon decoys and sensor-obscuring aerosols in this period. And between 1965 and 1970, ABRES would oversee the completion of three successful countermeasures systems for Air Force and Navy weapons. For Minuteman, the Air Force designed the Mk-1A chaff dispenser and Mk-12 countermeasure system; for Polaris, the Navy procured the ‘Antelope’ countermeasures suite. Both Antelope and the Mk-1A were adopted in 1969, while the Mk-12 was completed by the early 1970s.
Yet defense leaders’ interest in countermeasures began to slowly decline through the late 1960s. With a BMD moratorium on the horizon, senior officials found little reason to continue penaid efforts at their current pace. After intelligence suggested that the Hen House radar — a centerpiece of Soviet missile defense — lacked the range resolution necessary to target U.S. warheads, the Department of Defense postponed several decoy programmes through 1970.
Moreover, fruitful research into MIRVs had begun to displace countermeasures research and development. In 1965, the panelists of an Advanced Research Projects Agency study concluded that MIRVing was the most reliable mode for penetrating Soviet BMD. Titled Pen-X, the study’s findings significantly influenced Pentagon thinking. Indeed, by 1967, the Navy’s Special Projects Office eschewed deployment of penetration aids on the Poseidon missile, viewing its capacity for up to fourteen MIRVs as sufficient for overwhelming future Soviet defenses. In short, penaid research would be sidelined until the early 1980s — even as ABRES successfully tested thrusted replica decoys in 1975 and maneuvering reentry vehicles (MaRVs) in 1976.
Yet by the 1980s, ABRES and its sister programs had begun to rebuild momentum. By the decade’s conclusion, ABRES — incorporated into the broader Advanced Strategic Missile Systems (ASMS) program — had undertaken “significant works…on improving decoy and countermeasure designs,” flight testing numerous penetration aids. In 1985, for example, ASMS made significant improvements to Minuteman III’s countermeasures suite, optimizing decoys to simulate most signatures of real warheads. From 1980 onward, the project successfully flight tested systems including the Mk-500 decoy, a Navy-specific countermeasure, the Electronic Replica Decoy, which emitted false radar returns, Pyrotechnic Plume Decoys, which emitted false infrared returns, advanced thrusted replica decoys (TREPs), which accelerated through reentry, and the Evader MaRV, which replicated the angular motion, angle of attack, and thermal signature of genuine reentry vehicles. Additionally, ASMS intensively developed advanced chaff dispensers, flight testing “well over a dozen chaff payloads” throughout this timeframe. By the end of the decade, ASMS had built and tested dozens of exotic concepts — a far cry from the slowdown in the 1970s.
After 1990, however, the status of U.S. penaid programs has become difficult to ascertain. The names, budgets, and details of today’s countermeasures programs remain entirely classified. Meanwhile, other relevant sources — like the Missile Defense Agency (MDA)’s images of missile defense test targets — may not necessarily represent systems currently in use. Had those targets resembled actual countermeasures, the MDA would have had little motivation to present them openly. Accordingly, the agency classified all relevant test data once it began employing more operationally realistic test targets in 2002.
Nonetheless, historical U.S. penetration aids programs are unusually well-documented, shedding necessary light on the nuances and frustrations of countermeasures development. The following sections develop three themes from this richly preserved history.
Throughout its existence, both OSD and ABRES concurred that countermeasures development was unusually “difficult, time consuming, and expensive.” At the time, the phenomenology of midcourse maneuvering and ballistic re-entry was poorly understood; the underlying science would need to be investigated from scratch. Like their British counterparts, U.S. engineers would struggle with frequent delays and flight test failures, costing billions of dollars (unadjusted) per annum from 1958 until the early 1970s.
In its early stages, the U.S. penetration aid program encountered frequent technical setbacks. A 1966 project to create low-observable reentry vehicles, for example, took over a decade to meet its performance goals. Even purportedly “simple” countermeasures like chaff and decoys were notoriously difficult to perfect. Early chaff dispensers like the MK-1 required costly revisions to achieve uniform dispersal, while its successor, the MK-12 penetration aid, incurred over $68.8 (unadjusted) million in budget overruns from 1963 to 1967. In short, early penaids development was prohibitively expensive. While the MK-12 and its successors eventually matured, success only came after a long string of technical and budgetary setbacks.
Testing countermeasures was equally challenging. To assess decoy performance, range instruments needed extensive modifications to replicate Soviet defensive radars. In an effort to track reentry vehicles and dispersed chaff, for example, the Army spent millions enlarging test facilities at Kwajalein Atoll. Flight testing also proved to be particularly costly. By 1964, a “sizeable portion” of ABRES’ budget was spent on test rockets and their associated range fees — with each test costing as much as “$100 million each” by 1991. For states which lack established rocket industries, flight testing penaids may be unaffordable. Though potentially easy to construct, even the simplest countermeasures can be extremely expensive to validate.
II. MIRVs as Substitutes
The U.S. case also suggests that defense establishments often prioritize MIRVing over countermeasures development. As early as 1964, writes Greenwood, “support within the Air Force technical community had swung sharply away from decoys and toward MIRV.” After concluding that “MIRVs had several advantages” over decoy systems, the defense establishment largely pivoted away from penaids. While the United States still deployed countermeasures to hedge against Soviet missile defense breakthroughs, they substantially deprioritized their development.
To senior decisionmakers, the advantages of MIRV were obvious. First, there were few tradeoffs in selecting between MIRVs or penetration aids. They already shared significant technologies: the post-boost-vehicle concept used for MIRV, for example, was originally envisioned as a means of deploying decoys. Moreover, they already imposed similar weight penalties; much like a MIRV bus, “chaff and decoys were bulky”, and could “increase [payload] weight by a factor of about three.” In brief, adding a MIRVed warhead was “almost like putting a weapon inside of a decoy” — similar in cost, but markedly more effective.
Defense planners also considered MIRVs to be a more reliable means to penetrate enemy BMD. MIRVs’ failure modes were a known quantity: to defeat more warheads, the USSR would need to expend more defensive interceptors. Not so with penaids — unlike with MIRV, decoys and chaff might be defeated by unobservable changes in Soviet discrimination software. In view of these challenges, the Strategic Air Command and Department of Defense Research and Engineering became “convinced that chaff and passive decoys would soon become obsolete.” These concerns resurfaced again in the 1970s, with Department of Defense analysts concluding that the “flexibility of the software…coupled with the leadtime for penaid development” would pose a key weakness for penetration aids. While a Soviet response to MIRVing could be detected and accounted for, U.S. planners concluded that the obsolescence of penaids would be difficult to ascertain “short of fighting a war.”
Consequently, penetration aids never became a strategic priority. Indeed, in 1991 former officials reported that, in light of MIRV, “the PENAIDS program had been underfunded through most of its life.” Though the countermeasures effort was costly in its early years, the budgets it commanded through the 1970s were an insignificant fraction of total spending. While the countermeasures effort survived through the 1980s, it did not survive for the sake of the military advantages it conferred.
States desiring high-confidence penetration are likely to reach the same conclusions the Air Force did in 1969 — that “an all-RV attack, with no pen aids, is the least risky approach against a sophisticated area and terminal defense system.”Provided they can sufficiently miniaturize nuclear warheads, maturing nuclear powers are likely to prefer MIRVs over advanced penetration aids. Countermeasures are attractive tools so long as alternatives do not exist; in the U.S. case, penetration aids soon ceased to be a military priority after better alternatives emerged.
III. Bureaucratic politics
What motivated the U.S. decision to procure penaids, and how did these underlying logics change over time? As previously demonstrated, U.S. leadership increasingly viewed penetration aids as having marginal military utility through the 1970s. Though military and strategic considerations initially drove penaid procurement, the countermeasures program’s institutional linkages with larger programs — especially the Strategic Defense Initiative — was instrumental to its survival.
External-security considerations underpinned the United States’ early decisions to develop penetration aids. Accordingly, all three feasibility study groups independently concluded that penetration aids were a strategic necessity.Anticipating Soviet withdrawal from the Anti-Ballistic Missile Treaty, the Pentagon viewed penaids as “long-term insurance” against Soviet cheating. Bureaucracy-focused logics cannot sufficiently explain these behaviours. No individual bureaucratic entity lobbied the DoD to proceed; a broad-based element of the U.S. defense community justified penetration aids as a strategic imperative. Moreover, initial decisions to produce penaids did not stem from parochial needs; the program was instead a consensus response among several bureaucratic actors to an emerging Soviet threat.
By the 1970s, this explanation no longer seemed to apply. While analysts assumed in retrospect that American penaid development solely responded to “the intensity of Soviet development of ABM technologies,” the urgency of countermeasures programs did not perfectly correspond with perceived changes in Soviet capabilities. By then, Soviet BMD had proven far less effective than anticipated and the ABM Treaty far more so. Further, changes in technology and doctrine made MIRV an increasingly viable substitute to advanced penetration aids. Yet countermeasures programs would somehow survive. Despite completely eschewing countermeasures for the Poseidon SLBM, for example, Navy leadership would publicly testify that penetration aids would remain under development. As Soviet missile defense declined, U.S. countermeasures would improbably stay afloat.
Without a powerful strategic rationale to exist, ABRES and related programs survived through entanglement with larger bureaucratic coalitions. Through the 1960s, countermeasures and missile defense programs would enter an increasingly symbiotic relationship. As Pentagon officials noted at the time, countermeasures R&D was in large part “driven…by [the U.S.’] own ABM [Anti-ballistic missile] technology” — sharing funding, facilities, and personnel with BMD programs. And by the 1980s, BMD researchers would become penaids’ greatest advocates, demanding “more experimentation” to bolster countermeasures development.
Flight testing programs illustrate one element of these institutional overlaps. Just as effective penetration aids needed to be “observed by a radar very similar to that used by the defense,” realistic BMD testing required sophisticated countermeasures to test their capabilities. Range infrastructure programs like Defender and TRADEX, for example, were intended both to track BMD tests and assess decoy performance. Given their related mission sets, the respective programs became mutually indispensable. Entering a defensive clinch with missile defense efforts, U.S. countermeasures research could endure.
To conclude, weapons development does not solely respond to strategic imperatives. Even as the Soviet threat declined, BMD research pulled U.S. countermeasures programs along. Absent such a powerful BMD-oriented establishment, it is unlikely that the United States would have invested in advanced penaids past the 1970s.
In many respects, the United States’ experience is not unique. All of the United States’ Cold War contemporaries developed countermeasures of some form. And both the United Kingdom and Soviet Union certainly faced similar technical hurdles in developing countermeasures, with the Soviets spending heavily on constructing the full spectrum of “BMD penetration aids packages, including active jamming devices, dipolar reflectors, and light and heavy decoys.”Though information on foreign cases is sparse, it is likely that all major powers have encountered similar technical challenges to the United States in developing penetration aids.
Yet other facets of the U.S. experience appear exclusive to its institutional and cultural landscape. Specifically, it is unclear if other states share the hedging impulses U.S. planners felt, with their emphasis on overmatching the enemy in all possible contingencies. Concerned over an unexpected breakthrough in Soviet BMD, ABRES and the services explored dozens of exotic penaid concepts to hedge against unlikely scenarios.
Other states may not share these impulses. As Lewis and others note, Chinese strategists appear satisfied with a limited countermeasures program consistent with their strategy of minimum deterrence. In the past decades, China has certainly pursued a large spectrum of countermeasures technologies — including maneuvering, shrouded, and hardened reentry vehicles — to defeat U.S. missile defense. However, reports indicate that Chinese countermeasures development has largely focused on theater weapons systems — consistent with the People’s Liberation Army Rocket Force’s growing interest in conventional precision strike. Tellingly, while China began its countermeasures effort as early as 1966, it did not — like the Soviet Union or United States — go on to develop advanced decoys, deeming them far “too heavy for the DF-5.” Without such a maximalist view of contingency planning, states like China may not have develop countermeasures as intensively as the United States.
That said, countermeasures remain attractive at lower levels of technical sophistication. Basic exoatmospheric countermeasures — balloon decoys, chaff — are well “within reach of even fledgling missile powers,” and dovetail well with asymmetric strategies to introduce uncertainty in the United States and its allies.
In many respects, the technical challenges to acquiring low-end countermeasures may be less than what the United States historically faced. Engineers today benefit from a modern knowledge base; where the United States spent billions discovering the prerequisite rocketry and materials technologies during the Cold War, modern programs have faced fewer scientific bottlenecks.
In addition, developing nuclear powers could purchase relevant technologies from third parties. Research, development, and the acquisition of test data — not manufacturing — absorbs a large share of program cost, making technology transfer particularly attractive. Despite little evidence confirming such transfers, emerging powers have likely attempted them covertly. Indeed, Stokes has suggested that, as late as the mid-1990s, Russia had already exported several penetration aids to developing states.
Even with limited resources, opaque regimes like North Korea remain concerned with U.S. and allied missile defense. Though their strategic cultures are occasionally difficult to glean, emerging powers will — given their resource limitations and small delivery vehicle stockpiles — likely settle for low-tier countermeasures to fulfill their deterrence requirements. Rather than investing enormous sums for sophisticated penetration aids, these states will calculate that U.S. leaders cannot tolerate the small uncertainties that such systems would induce.
Though assessing foreign countermeasures remains a challenge for open-source analysts, the U.S. case study generates several major conclusions for future scholarship. First, the U.S program encountered many technical surprises — far more than scholars anticipate. Moreover, U.S. leadership overwhelmingly viewed penetration aids as an imperfect alternative to MIRV. And finally, the U.S. program was not solely motivated by strategic concerns, driven instead by powerful bureaucratic forces within the missile defense community.
The uncertainties which penetration aids generate pose a major problem for deterrence. But absent more open-source literature on foreign countermeasures, it becomes difficult for political stakeholders to reassure allies or realistically evaluate national missile defense strategies. As the United States prepares to invest significantly in its BMD program, this problem has only become more salient.
While Sessler, Grego, and others have developed robust technical assessments of potential countermeasures, more case studies of historical countermeasures programs — particularly of emerging powers like China — would greatly contribute to the missile defense discourse. The reality of strategic weapons procurement often diverges from hypotheticals. As emerging nuclear states acquire simple exoatmospheric countermeasures, the U.S. case presents an example of the constraints they may face in the long term. Scholars are right to highlight how effective countermeasures can be. The time is now ripe to examine the far messier process of acquiring them.
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 Ibid; Andrew M. Sessler et al., Countermeasures: A Technical Evaluation of the Operational Effectiveness of the Planned US National Missile Defense System, (Cambridge: Union of Concerned Scientists, 2000), <https://www.ucsusa.org/sites/default/files/legacy/assets/documents/nwgs/cm_all.pdf>.
 Ibid; Andrew S. Erickson, “China’s space development history: A comparison of the rocket and satellite sectors,” Acta Astronautica, №103 (2014), pp. 142–167; Robert S. Norris et al., Nuclear Weapons Databook, Volume V: British, French, and Chinese Nuclear Weapons, (Boulder: Westview Press, 1994), ISBN: 081331612X; Helen Parr, “The British Decision to Upgrade Polaris, 1970–4,” Contemporary European History, №22, Vol. 2 (2013), pp. 253–274.
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 Ted Greenwood, Making the MIRV: A Study of Defense Decision Making, (Cambridge: Ballinger, 1975); Donald Mackenzie, Inventing Accuracy: A Historical Sociology of Nuclear Missile Guidance, (Boston: MIT Press, January 1993); Graham Spinardi, From Polaris to Trident: The Development of U.S. Fleet Ballistic Missile Technology, (Cambridge: Cambridge University Press, 1994).
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 Ibid; Boeing Corporation, “Technical Manual, Operation Instructions, Minuteman Weapon System,” Technical Order 21M-LGM30G-1–13, United States Air Force, June 9, 1995; Richard A. Hartunian, “Ballistic Missiles and Reentry Systems: The Critical Years,” Crosslink, Winter 2003, <https://web.archive.org/web/20030410002921/http://aero.org/publications/crosslink/winter2003/02.html>; U.S. Air Force, Historical Division Liaison Office, “USAF Ballistic Missile Programs 1964–1966,” by Bernard C. Nalty, File Copy 80-CVAH(S)-D233/680/-8A, 1967, <http://tinyurl.galegroup.com/tinyurl/5w6nW0>.
 Atta et al., “Darpa Technical Accomplishments Volume II,” pp. 4–5, 4–6; Greenwood, Making the MIRV, Ch. 4.
 Ibid; Brendan Rittenhouse Green and Austin Long, “ The Geopolitical Origins of US Hard-Target-Kill Counterforce Capabilities and MIRVs” in The Lure and Pitfalls of MIRVs: From the First to the Second Nuclear Age, ed. By Michael Krepon et al., (Washington: Stimson Center, 2016), <https://www.stimson.org/sites/default/files/file-attachments/Lure_and_Pitfalls_of_MIRVs.pdf>; U.S. Congress, Senate, Subcommittee of the Committee on Appropriations, On H.R. 15090, an act making appropriations for the Department of Defense for the fiscal year ending June 30, 1970, and for other purposes, 91st Cong., 1st sess., (1969), pp. 371–376, <http://hdl.handle.net/2027/uc1.b3636870>.
 Ibid; Lin, “Development of U.S. Air Force Intercontinental Ballistic Missile Weapon Systems,” pp. 504–507; U.S. Air Force, History Support Office, “Space and Missile Systems Organization: A Chronology, 1954–1979,” by John T. Greenwood, October 1979, <http://www.dtic.mil/dtic/tr/fulltext/u2/a369676.pdf>.
 USAF, “USAF Ballistic Missile Programs 1964–1966,” p. 41.
 Lin, “Development of U.S. Air Force Intercontinental Ballistic Missile Weapon Systems,” pp. 504–507.
 Ibid; W.S. Kennedy et al., “Solid Rocket Motor Development for Land-based Intercontinental Ballistic Missiles,” Journal of Spacecraft and Rockets Vol. 36, №6 (1999), pp. 890–901.
 Theresa Hitchens, “Trust but Verify, What Will New Missile Test Secrecy Hide?” Defense News, May 27, 2002; Ted Postol and George Lewis, “Briefing to the National Research Council Committee on An Assessment of Concepts and Systems for U.S. Boost-Phase Missile Defense in Comparison to Other Alternatives,” Washington, D.C., May 19, 2010, < http://web.mit.edu/stgs/pdfs/NAS_Slides__May18,2010_2x1.pdf>
 Senate, On H.R. 15090, p. 375.
Atta et al., “Darpa Technical Accomplishments Volume II,” p. 1–26; Baylis and Stoddart, “Britain and the Chevaline Project,” pp. 1, 133–146; Andrew S. Erickson, “China’s BMD Countermeasures: Breaching America’s Great Wall in Space?” in China’s Nuclear Force Modernization, edited by Lyle J. Goldstein, (Newport: Naval War College, 2005), pp. 65–194; Jerry Friedheim to Larry Lynn, “Questions and answers relating to the U.S. military budget for weapons systems needed to protect the U.S. from possible Soviet aggression,” Memorandum, n.d., <http://tinyurl.galegroup.com/tinyurl/6hadg4>; U.S. Department of Defense, “Draft Presidential Memorandum on Strategic Offensive and Defensive Forces,” OSD Control CCS X-0155, January 9, 1969, <http://tinyurl.galegroup.com/tinyurl/6hanQ8>.
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 Unadjusted cost
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 Greenwood, Making the MIRV, p. 41.
 U.S. Office of Technology Assessment, “SDI — Technology, Survivability and Software,” Report No. OTA-ISC-353, May 1, 1988, p. 149, <https://ota.fas.org/reports/8837.pdf>.
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