Last Friday, British newspapers reported that the U.S. had agreed to supply Russia with sensitive information on Britain’s nuclear deterrent in order to win Russian agreement to New START. Over the weekend, State Department spokesman P.J. Crowley described this claim as “bunk” and asserted that New START simply “carried forward and updated this notification procedure to the new treaty” from the 1991 START.

The WikiLeaks document on which the original story was based—and the treaties of 1991 and 2011—tell a different story. The 1991 treaty requires notification of the transfer of items (such as the U.S.-made Trident II missiles on which Britain’s nuclear force relies). This notification must include “the number and type of items transferred; the date of transfer; and the location of transfer.”

New START, on the other hand, requires that the “number, type, date, unique identifier, and location of the transferred [missiles] must be provided.” In short, New START goes further than the original START in at least two ways.

First, the U.S. must now provide the Russians with a “unique identifier” for each transferred missile. As the U.S. negotiator states in the WikiLeaks cable, “this was more information than was disclosed under START.” Over time, this information will allow the Russians to build up a more complete picture of the size of the U.K.’s active nuclear force, information that Britain has deliberately kept secret.

Second, the U.S. must now tell the Russians not where the transfer took place but where the transferred items will be kept. This distinction is crucial. Contrary to Crowley’s statement, the 2011 treaty imposes a new and much more exacting requirement on the U.S. Under the 1991 treaty, the U.S. could simply state that the missiles were transferred to Britain in, for example, Norfolk. Now, the U.S. is obligated to tell Russia where the British will store and deploy the missiles.

This is important for two reasons. First, the U.K.’s deterrent force, like the U.S.’s, relies for its safety and survivability on the fact that possible adversaries do not know where it is and hence cannot target and destroy it. New START’s provisions eat into that protective veil of secrecy. Second, New START’s provisions obligate the U.S. to tell Russia about facilities inside Britain. This implies that Britain’s defenses are not fully its own and that Britain is not independent and sovereign in this nuclear realm. Nor do we know how the U.S. plans to fulfill this obligation. A general statement about Britain’s facilities would be bad enough, but if the U.S. passed on detailed information, that would be extremely damaging to the effectiveness of the U.K.’s deterrent.

The WikiLeaks revelation is troubling for many other reasons. It is receiving scrutiny now only because of these unauthorized leaks: If the Senate had been provided with the full negotiating record, the importance of this sharing of British information could have been debated by the Senate. In particular, it is not clear if New START is compatible with the 1958 U.S.–U.K. Mutual Defence Agreement, which (except in certain specifically authorized circumstances) precludes the U.S. transfer to third parties—such as Russia—of U.K. nuclear information. If New START is incompatible with the 1958 agreement, then New START is an explosive breach of a fundamental and longstanding U.S. treaty obligation. More broadly, we do not know what other information about U.S. relations with other allies the U.S. has promised to disclose to the Russians.

It also shows that the Russians have not given up on their Cold War tactic of seeking to treat Britain as an American subsidiary. Time and again during the Cold War, the Soviets argued that Britain’s defenses were just an extension of the U.S.’s and that Britain was not a fully sovereign country. The U.S. always rejected that contention and kept U.S.–Soviet negotiations strictly bilateral. Now, by agreeing to provide information about where Britain keeps its missiles, the U.S. has conceded part of the Soviet argument. This is a profoundly undesirable departure from decades of precedent and alliance diplomacy, which treated members of NATO as closely cooperating but nonetheless sovereign and independent states.

Finally, the WikiLeaks cable shows that the Russians are now also seeking to use arms control negotiations as a lever to break down the close ties between the U.S. and Britain. The Russian negotiator is quoted as complaining that “Russia did not have an agreement with the U.K. to provide notification when the U.K. performed a test flight.” The U.S. negotiator responded (admirably) that that was not the U.S.’s problem. But the Russian negotiator was laying down an argument: If you want more arms control agreements in the future—and the Administration does indeed want more agreements—you cannot have them as long as we cannot inspect and control the close ties you have with Britain. In short, future agreements will come at the expense of the Anglo–American Special Relationship.

The provisions of New START do not simply carry forward those of 1991. They are different, they are more extensive, they raise legitimate questions about what else we do not know, they undermine the secrecy—and thus the effectiveness—of Britain’s nuclear deterrent, and the negotiating record as disclosed by WikiLeaks implies that the Russians view them as a way to break down the core of the Atlantic Alliance. For all these reasons, the WikiLeaks disclosures are profoundly troubling and should be the subject of detailed congressional investigation.