UK, U.S. Seek Indefinite Extension of Nuclear Cooperation Pact

October 2024
By Shizuka Kuramitsu

The United Kingdom and the United States, responding to perceived rising threats, are seeking to bolster nuclear cooperation by indefinitely extending their mutual defense agreement prior to its expiration at the end of the year.

On July 25, Karen Pierce, the UK ambassador to the United States, and Bonnie Jenkins, the U.S. undersecretary of state for arms control and international security, signed a pledge to amend the agreement. The UK Parliament and the U.S. Congress are now considering acting on the amendment, which includes a clause deleting references to the expiry date.

The mutual defense agreement has allowed the two allies to exchange nuclear materials, technology, and information related to nuclear weapons, naval nuclear propulsion, and nuclear threat reduction since 1958 and has been renewed several times.

The agreement underpins the special UK-U.S. defense relationship and is considered unique among nuclear-weapon states because of the level of dependency and technical integration. Areas of recent collaboration include nuclear weapons modernization projects and safeguards.

By extending the agreement indefinitely, the proposed amendment streamlines the UK-U.S. exchange of nuclear materials and components of nuclear weapons and submarine reactors. “The exception to this is information sharing, which either state can end unilaterally at certain times if they give one year’s notice,” according to a report on Sept. 11 by Nuclear Information Service, a UK think tank.

The change fosters bilateral nuclear cooperation amid rising nuclear threats from their adversaries, namely Russia and China. David Cullen, director of the Nuclear Information Service, told the Financial Times on Sept. 2 that the amendment “provides a permanent underpin to the modernization of the UK’s nuclear deterrent.”

“It also locks in cooperation over AUKUS,” he said, referring to the Australia-UK-U.S. agreement to supply Australia with nuclear-powered submarines and other defense cooperation.

Discussing the agreement at an event in Washington on July 29, Jill Hruby, administrator of the U.S. National Nuclear Security Administration, said that the two countries “are closely aligned, with our W93 [nuclear warhead] program and their [UK] replacement warhead program Astraea.”

The allies also “are working together to create a new development and training center for [International Atomic Energy Agency] safeguards, and we are discussing a mutual resilience strategy for our nuclear deterrence, and importantly…we are working to provide Australia with a nuclear-powered, conventionally armed submarine capability under the AUKUS agreement,” Hruby added.

The amended agreement was submitted to the UK and U.S. legislative bodies in July.

The amendment is “consistent…with United States commitments to the United Kingdom regarding the development and deployment of the United Kingdom TRIDENT Strategic Weapon System, continued cooperation in nuclear propulsion programs, and support for the United Kingdom atomic weapon and nuclear threat reduction programs,” U.S. President Joe Biden said in a letter to Congress on July 29.

Sens. Tim Kaine (D-Va.), Deb Fischer (R-Neb.), Tom Cotton (R-Ark.), and Angus King (I-Maine) proposed an amendment extending the agreement as part of the National Defense Authorization Act for fiscal year 2025. The amendment must be approved by both houses of Congress.

In the UK, the amended agreement was presented to Parliament on July 26. It will be enacted automatically unless the House of Commons or the House of Lords passes a resolution objecting to the amendment before Oct. 23.

On Sept. 2, seven members of Parliament requested a parliamentary debate, called an Early Day Motion, due to concerns that the extension “violates both countries’ obligations” under the nuclear Nonproliferation Treaty (NPT).

The explanatory memorandum attached to the amendment signed by John Healey, the UK defense secretary, on July 26 says that the agreement “does not provide for the transfer of nuclear weapons or other nuclear explosive devices, or control over such weapons or explosive devices” and therefore “[o]ur cooperation under the [agreement] is consistent with the UK's obligations” under the NPT.