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Reagan and Thatcher
Long before Ronald Reagan offered Margaret Thatcher hundreds of millions of R&D funding associated with SDI, she supported the program, often over the objections of others in the British government. (credit: Reagan Library)

The secret history of Britain’s involvement in the Strategic Defense Initiative

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In March 1983, President Ronald Reagan surprised the world when he called upon American scientists to use their talents to render ballistic missiles “impotent and obsolete.” His speech would lead to the establishment of the Strategic Defense Initiative (SDI), derisively called “Star Wars.” It grew into a $30 billion effort to explore the technologies required for a multi-layered missile defense system with land, sea, air, and space-based interceptors. While SDI looms large in Cold War political histories, very little has been actually written about the system itself and how it evolved over time. Even less has been written about the involvement of foreign countries in SDI research and development.[1] Of all the foreign participants, the United Kingdom was the most significant in terms of its political value for the Untied States and its access to highly classified areas of SDI research.

Thatcher regularly read Aviation Week and Space Technology when she was leader of the opposition in the British Parliament and took a special interest in articles about Soviet research into directed energy weapons that could be used for both anti-satellite weapons and missile defense.

Political histories of the 1980s often portray British Prime Minister Margaret Thatcher as having been opposed to SDI, then having her mind changed by a US offer of hundreds of millions of research and development dollars in exchange for British support for the program.[2] Recently declassified British documents reveal a very different story. Thatcher believed that SDI was a strategic imperative as a hedge against a Soviet break-out in strategic defenses. She moreover maintained that the United States needed to stay ahead of the USSR in military space technologies across the board. The prime minister viewed SDI research as a way to stay up to date on the latest missile defense technologies in an effort to keep the British nuclear deterrent credible well into the 21st century. Notably, her advisors consistently disagreed with her support for SDI and were vehemently opposed to it on the grounds that it would lead to an arms race in space and undermine the credibility of the UK nuclear deterrent.

Thatcher’s concern about missile defense and military space technologies long predated her tenure as prime minister. She had regularly read Aviation Week and Space Technology when she was leader of the opposition in the British Parliament (February 1975 to May 1979). She took a special interest in articles about Soviet research into directed energy weapons that could be used for both anti-satellite weapons and missile defense. Thatcher was undoubtedly aware of the 1977 Aviation Week and Space Technology article claiming that that the Soviets were nearing a breakthrough with a laser “capable of neutralizing the entire United States ballistic missile force.”[3] The prime minister later said that, due to her close following of media reporting and analysis on Soviet laser research, she concluded that the Soviet Union might be getting ahead of the West and could “upset the whole [strategic] balance.”

In the 1980s, Britain was especially worried about the implications of advances in missile defense for the credibility of its nuclear deterrent. Since the early 1970s, the United Kingdom had a secret program called Chevaline that involved the development of penetration aids for its Polaris submarine-launched ballistic missiles to ensure that their warheads could get through Soviet missile defenses around Moscow. In 1982, Thatcher secured an agreement to purchase the upgraded US Trident II submarine-launched ballistic missile system. The decision to obtain Trident was especially controversial due to cost and rising anti-nuclear sentiments in Britain. Furthermore, anything, like advances in missile defense, that could even appear to undermine the credibility of the UK strategic deterrent was of great concern to Thatcher and her advisors.

On March 23, 1983, Reagan made his “Star Wars” speech during a televised address to the nation. No allies were consulted ahead of time. Given the importance of nuclear deterrence to the British, they were especially concerned about his call to render ballistic missiles obsolete. Within a few days of the speech, the British Ministry of Defence submitted a classified analysis of it to Thatcher. It concluded that “there is nothing in the laws of physics to prevent the deployment of space-based energy weapons…” and that “it would probably take at least ten years to define the requirements….and at least another twenty to develop and deploy it.”[4] The report went on to say that the Soviets could produce more anti-satellite weapons to destroy the missile defense components in space. The Ministry of Defence cautioned that Trident would likely not be completely impacted by SDI because there was a low probability that strategic defense technologies would mature before the year 2010.[5]

At the time of SDI’s formal establishment as a defense program in January, 1984, the British Foreign Office and Ministry of Defence were increasingly concerned about an arms race in space. They wanted Thatcher to put pressure on Reagan to restrain the development of both anti-satellite weapons and SDI; the United States was working on an air-launched anti-satellite called the Miniature Homing Vehicle. British defense, diplomatic, and intelligence officials wanted to constrain a space arms competition because they recognized that Britain was especially dependent on the United States for intelligence collected by reconnaissance satellites. They believed that missile defense in space and anti-satellite weapons would provoke the Soviets to develop more of their own anti-satellite systems that would make US space reconnaissance satellites even more vulnerable.

There was a belief, in at least some corners of the British defense establishment, that military space technologies could seriously alter the strategic situation.

British dependence on US space reconnaissance became even more apparent after the 1982 Falklands War.[6] Senior UK national security officials worried that if they opposed anti-satellite weapons and SDI then the United States might reduce, or even cut off, British access to US space reconnaissance assets. Consequently, in developing policy positions on both anti-satellite weapons and SDI, the Foreign Office and Ministry of Defence consistently highlighted Britain’s “dependence on US space-derived intelligence” and the requirement not to upset this arrangement.[7]

Despite these serious national security concerns surrounding SDI and anti-satellites, Thatcher pushed back on her advisors’ recommendations to attempt to rein in the development of space weapons. The prime minister stated that she did not want to encourage Reagan to consider controls on anti-satellites.[8] Even though many European leaders were in favor of limits on space weapons, she was opposed to any agreements that would “prevent the Americans from reaching parity [with the USSR] in low altitude ASATs [anti-satellites].”[9] Additionally, she recognized that a ban on anti-satellites would hamper the development of SDI because of the technological linkage between the two, and she therefore refused to adopt a negative policy position in this general area.

Policy decisions also had to be reconciled with the potential future military applications of space systems. There was a belief, in at least some corners of the British defense establishment, that military space technologies could seriously alter the strategic situation. A classified study on the implications of missile defense technologies stated that “it would be historically unprecedented if, after 50 years of accelerating technical change, the nuclear tipped ballistic missile were to remain the single unchallengeable ultimate weapons [sic] into the early twenty first century.”[10] The report argued that SDI-related research could have important consequences for the domination of space and that the Soviets were ahead of the United States in key areas of directed-energy weapons research. The authors of the study maintained that:

The need to employ it [missile defense] in space should give the US – and thus the West – an advantage in that increasingly important ‘high frontier’ area of military operations and economic competition. The alternative could be the inexorable attainment of a ‘Pax Sovietica’ based on the domination of space, just as the ‘Pax Britannica’ formerly rested on the control of the High Seas.[11]

This British space policy paper suggested that “if the UK is to remain a significant industrial and defense power, it will be necessary to have a competitive ability in appropriate space technology.”[12] Despite these observations, the ministers of defense and foreign affairs maintained that restraint was still the best option.

Thatcher continued to reject the opposition to SDI of her senior ministers and she emphatically stated that at the very least, “the Americans have little option but to push ahead at least to the point where they can be confident that they are matching the Soviet Union [in strategic defense].”[13] Thatcher was, however, very concerned about Reagan’s talk of using SDI to secure a nuclear-free world. She therefore refused to make any pronouncements on SDI until she had an opportunity to convince Reagan to say publicly that SDI would not be used as an instrument of nuclear abolitionism. Politically, she could not support an effort designed to render obsolete the nuclear weapons that were the foundation of British defense policy.

The Pentagon appointed US Air Force Lt. Gen. James Abrahamson to oversee SDI. Notably, he developed a very close relationship with Thatcher.

During a meeting at Camp David in late December 1984, Thatcher convinced Reagan to state publicly that SDI was a research program and that any deployment decision would be a matter for negotiation with the USSR. Most significantly, the president furthermore said that SDI would enhance, but not replace, deterrence. These points became known as the Camp David Declaration, and served as the basis for Thatcher’s public messaging on SDI. After the Camp David meeting, Thatcher turned her attention to getting Britain involved in SDI research and development.

Less than one month after the Camp David engagement, the UK ambassador in Washington, Oliver Wright, submitted a message to the Foreign Office outlining why Britain needed to become involved in SDI. Wright asked, “are we going to exclude ourselves from the revolution in defense technology that the SDI research program is likely to ignite?” He argued that there was a “real danger of our missing the bus” as Britain had “missed the space bus” previously. Additionally, there were going to be “spin-off[s] in many areas of defense, and no doubt civilian, technology also,” Wright predicted.[14]

Reagan wanted British participation in SDI to garner greater European support for his controversial effort. The Strategic Defense Initiative Organization (SDIO), which oversaw the program, was especially interested in working with British institutions researching optical computing. SDIO had concluded that optical computers were necessary to control the directed energy and kinetic weapons associated with SDI. Several of Thatcher’s advisors believed that SDI research in computing (and other areas) could be used to further Britain’s conventional military capabilities and industrial competitiveness. Fundamentally, defense, industrial, and political interests were inseparable in the British motivation for involvement in SDI. After nearly a year of negotiations, on December 6, 1985, the United States and the United Kingdom signed a formal memorandum of understanding solidifying Britain’s participation.

The Pentagon appointed US Air Force Lt. Gen. James Abrahamson, a former member of the Manned Orbiting Laboratory program, to oversee SDI. Notably, he developed a very close relationship with Thatcher. Multiple times per year he would travel to the United Kingdom and brief her about recent technological developments and provide intelligence on Soviet missile defense and military space programs. According to Charles Powell, one of the prime minister’s closest advisors, Thatcher was “entranced by the [Abrahamson] briefings” and as a result, “she grew steadily more favorable to [SDI].” Consequently, the prime minister had such confidence in Abrahamson that he “pretty well had a regular pass to Number 10 Downing Street for several years, to come and tell us about every latest development.”[15]

By early 1987, SDI had undergone serious transformations. The Pentagon had endorsed a strategic defense system phase-one plan that US Secretary of Defense Caspar Weinberger said could be deployed in the early 1990s.[16] This version of SDI was scaled down and excluded lasers and focused instead on ground- and space-based kinetic interceptors. Deployment would have required either abrogation or a re-negotiation of the 1972 Anti-Ballistic Missile (ABM) Treaty that prohibited missile defense in space. The Foreign Office and Ministry of Defence once again raised their opposition to deployment. Even well into 1987, the prime minister had been very nervous about the implications of SDI for the ABM Treaty. As Abrahamson convinced her that SDI technologies were advancing, she became more supportive of potentially moving beyond the treaty restrictions at some point. Consequently, Thatcher informed Reagan that if the feasibility of SDI could be established through testing, then she would support negotiations with the Soviet Union regarding the ABM Treaty. Fundamentally, she believed that a breakthrough with missile defense was around the corner, and she wanted to ensure that the United States (and Britain by extension) kept at the forefront of technological development.

Through her contact with Abrahamson, it was clear to Thatcher that a strategic defense system would not be able to fully replace nuclear deterrence, at least not in the foreseeable future. Abrahamson provided to Thatcher the Joint Chiefs of Staff criteria for a phase-one system. They required that it “be capable of destroying 50% of the first wave of SS-18s [based on pre-START numbers] and 30% of other systems.”[17] Strategically, Thatcher concluded that SDI would upset the Soviet calculus and was also important as “a hedge against nuclear attack by some maverick power such as Libya or North Korea.”[18] She recognized, however, that there were still serious technical obstacles, especially with the command and control software, to creating a functioning missile defense system.

Even though the Ministry of Defence benefited from SDI involvement, senior officials wanted to use Reagan’s 1989 departure from the presidency to rein in the program.

Even though senior British ministers remained opposed to SDI deployment, the Ministry of Defence saw an opportunity to use its involvement in the program to further the credibility of its nuclear deterrent. In particular, the defence minister sought American permission to test its anti-ballistic missile penetration aids using space-based sensors that were launched through the SDI research program. Thatcher wrote on the back of a memo outlining the defence minister’s request that “on this [proposal] – I think we had better go ahead… what alarms me is that we have no penetration aids for Trident and we may need some” [emphasis in the original][19] Consequently, through a secret Anglo-American effort codenamed Zodiac Beauchamp, the British were able to confirm that advanced missile defense tracking capabilities could not distinguish between their penetration aids and the actual warheads. This success gave the Ministry of Defence a high degree of certainty that the penetration aids would ensure that the warheads made it through Soviet missile defenses around Moscow.

Even though the Ministry of Defence benefited from SDI involvement, senior officials wanted to use Reagan’s 1989 departure from the presidency to rein in the program. After the election of George H.W. Bush, both the ministers of defence and foreign affairs lobbied Thatcher to express opposition to the deployment of SDI. By this point, the phase one SDI plan had been re-named Brilliant Pebbles. This concept involved placing into orbit hundreds of interceptors that could be used to destroy ballistic missiles. Abrahamson had convinced Thatcher that this system could be deployed in the mid-1990s. In reality, the requisite information technologies for command and control were still not yet even close to mature. Regardless of the technical difficulties, the ministers of defence and foreign affairs believed that even a partially functioning system would be highly destabilizing and provoke the Soviets into improving their own missile defenses. Such a move would have undermined, they argued, the credibility of the British deterrent.

Thatcher “disagreed strongly” with the recommendation of her ministers to push back on SDI. She said that “there were good arguments for eventual deployment of strategic defenses” and she once again highlighted SDI’s potential for upsetting the Soviet strategic calculus and thereby enhancing deterrence. More fundamentally, she emphasized that pushing forward with SDI was necessary to “remain ahead [of the USSR] in [advanced] technology.” Consequently, in her first meeting with President George H.W. Bush, the prime minister said that she was “glad to see the president remained committed to SDI” and he replied that “there was no question of trading it away, the administration would stay with it.”[20] In reality, Bush was not as ideologically tied to SDI as Reagan had been; he certainly did not see the program as a means of securing a nuclear free world.

As the Cold War came to an end, the scope and purpose of SDI began to change more rapidly. By 1991, SDI had been transformed into a simpler version called Global Protection Against Limited Strikes, which was designed to provide a very limited defense against accidental nuclear launches and rogue nuclear states. A mid-1990s deployment date looked even less likely because of technological obstacles and waning political support; space-based missile defense efforts would be fully eliminated by the Clinton Administration. After the dissolution of the USSR, President George H.W. Bush examined the possibility of sharing SDI-related missile defense research with Moscow as a means of bolstering relations with the Russian Federation. Thatcher’s successor, John Major, was unenthusiastic about strategic defense and he was vehemently opposed to giving SDI data to Moscow. Major drafted a letter to President Bush in which he said “[Russian president Boris] Yeltsin will not be with us forever…a future Russian government may not be as comfortable a partner for the West.”[21] He was, moreover, opposed to the Bush Administration’s interest in re-negotiating the ABM Treaty.[22] Fundamentally, even though the Cold War was over, space-based missile defense had become a more contentious subject in Anglo-American relations.


  1. Peter Westwick called for more research into the international dimensions of SDI. See; “The International History of the Strategic Defense Initiative: American Influence and Economic Competition in the Late Cold War”, Centaurus, 2010, Vol. 52, 341
  2. Archie Brown also repeats this narrative in his, The Human Factor: Gorbachev, Reagan, and Thatcher, and the End of the Cold War (Oxford: Oxford University Press, 2020), 141
  3. Robert Hotz, “Beam Weapon Threat,” Aviation Week and Space Technology, May 8, 1977.
  4. PREM 19/1188, MOD Letter to No. 10, “President’s Reagan’s Speech on Defensive Technology”, March 29, 1983, UK National Archives (TNA hereafter).
  5. Ibid
  6. For an overview of space reconnaissance and the Falklands, see Dwayne Day, The Lion and the Vortex, March 11, 2013, The Space Review.
  7. PREM 19/1188, Cradock letter to Powell on ASATs and arms control, July 2, 1984, TNA.
  8. PREM 19/1188, No. 10 record of conversation, July 16, 1984, TNA.
  9. PREM 19/1188, No. 10 record of conversation, July 16, 1984, TNA.
  10. PREM 19/1188, Heseltine and Howe Minute to MT, “Ballistic Missile Defence (BMD): UK Policy Towards the US Strategic Defence Initiative,” October 11, 1984, TNA.
  11. Ibid
  12. PREM 19/1413, Letter from the Royal Society to the PM, Annex E: “The Future of Space,” December 6, 1984, TNA.
  13. PREM 19/1188, No. 10 letter to MoD, UK Policy on SDI, October 15, 1984, TNA.
  14. PREM 19/1444, letter from Wright to Howe, January 29, 1985, TNA.
  15. Powell made this comment during a July 9, 2003, Centre for Contemporary British History oral history program. See for details: “The British Response to SDI,” ed., Michael D. Kandiah and Gillian Staerck, 2005, 32.
  16. Brad Smith, “Weinberger Suggets Early SDI Deployment,” January 23, 1987, UPI.
  17. PREM 19/2614, SDI Participation Office report on “SDI Programme Status” Feb 1988, TNA. According to this document, Strategic Defense System phase one would involve a boost/post-boost layer space tracking and space-based interceptors and a late-midcourse system that consisted of ground bases interceptors and space-based tracking.
  18. PREM 19/2614, Powell memo to the PM, December 23, 1988, TNA.
  19. PREM 29/2068, Powell memo for the PM, October 2, 1987, TNA.
  20. PREM 19/2890, No.10 conversation record, PM-Bush, June 1, 1989, TNA.
  21. PREM 19/3650, “Draft Letter from the Prime Minister to President Bush,” 1992, TNA.
  22. PREM 19/3650, Cradock letter to Mr. Wall, “GPALS,” May 29, 1992, TNA.

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