Defense Secretary Ashton Carter and Britain's Secretary of State for Defense Michael Fallon attended a NATO defense ministers meeting in Brussels this month. (Francois Lenoir/Reuters)

Defense leaders from both sides of the Atlantic scrambled this week to downplay the impact of Britain’s decision to leave the European Union, saying the United States’ closest military relationship would be sheltered from the upheaval that may lie ahead.

A British official said the United Kingdom remains committed to its membership in the North Atlantic Treaty Organization (NATO) and will continue to partner with the United States against the Islamic State and other shared threats.

“There clearly has been a significant impact over the last few days, and things will play out in the markets and elsewhere as they will,” said the official, who spoke on the condition of anonymity to frankly discuss his government’s position. “But from where I sit . . . we still intend to be the strongest nation in NATO that we possibly can be. The nature of our relationship with the U.S. has not changed one iota.”

An American defense official also staked out military ties as an area of the transatlantic relationship that would be largely shielded from the economic and political changes that may accompany Britain’s transition to a more solitary role along Europe’s western edge. He suggested that the widespread concerns about Brexit were overblown.

“We showed up to work the next day,” the official said.

President Obama has sought to deflate public anxiety. “There’s been a little bit of hysteria post-Brexit vote, as if somehow NATO’s gone, the transatlantic alliance is dissolving, and every country is rushing off to its own corner,” the president said in an interview with NPR that aired Tuesday. “That’s not what’s happening.”

But security experts warn that much remains unknown, even for senior government officials, about what real-world consequences may result from Britain’s departure from the E.U. in the relatively insulated world of military and security ties.

“We are writing a completely new chapter in Europe’s history,” said Heather Conley, a former State Department official who is now a scholar at the Center for Strategic and International Studies in Washington. “The uncertainty absolutely is going to be an all-absorbing activity for Europe and the U.K., and we don’t know what that impact will be.”

The vote, which stunned officials at the Pentagon and other government agencies across Washington, is likely to dominate next month’s NATO summit in Warsaw, potentially overshadowing discussion about ongoing conflicts in Ukraine and Afghanistan.

For decades, the United States has conferred on Britain, its most important military ally, more special military privileges than any other country. The U.S. government shares more intelligence with Britain than it does with other nations; Britain is now the only country to have lethal U.S. drone technology; and British military personnel can regularly be seen in the halls of the Pentagon.

“[What] came out of World War II and then got us through the Cold War was a very close defense and security relationship, one that is intertwined in a lot of ways,” the U.S. official said, also speaking on the condition of anonymity to discuss bilateral defense ties.

Since the attacks on Sept. 11, 2001, the Pentagon has relied on Britain’s much smaller but highly skilled military in operations across the globe. After 9/11, British troops joined their American peers in the NATO-led mission in Afghanistan, as they did in the U.S.-led war in Iraq. Today, both the United States and Britain have small numbers of elite forces in Libya.

Officials from both countries said the reason why the bilateral defense relationship will be relatively unchanged is that most of the two countries’ military cooperation takes place on a bilateral basis or through NATO. There are no major agreements or any military arrangements that will need to be renegotiated.

Speaking after the vote, British Defense Secretary Michael Fallon said his country will not back down from its duty to combat international threats.

“This is not Britain turning its back on the world,” he told Sky News. Today, Britain has more than 250 troops training and advising local forces in Iraq. According to British media reports, the government of Prime Minister David Cameron is considering augmenting its small military force in Afghanistan, in light of the Taliban’s resurgence there.

The next U.K. government, after Cameron steps down this fall, is sure to share European concerns about an increasingly assertive Russia and will likely continue, for the near term at least, its participation in an air policing mission in the Baltic region and other activities that seek to respond to Russian President Vladi­mir Putin’s military posture.

Fallon said Britain would announce a decision at the upcoming Warsaw summit to place troops closer to Europe’s eastern edge as a response to Russian actions there.

Evelyn Farkas, who served as a senior Pentagon official for Russia, Ukraine and Eurasia, said the difficult task of extricating Britain from the E.U. has the potential to distract European leaders from the ongoing conflict in Ukraine but ultimately will not change the British position against Russia’s expansionist moves.

“As much as Putin might be applauding this and pointing to the weaknesses and divisions within Europe . . . he’s not going to be able to reap much reward from this directly,” she said. “The Brits are just as much with us on the issue of Crimea and Ukraine . . . and this isn’t going to change that.”

Farkas said U.S. military leaders will, however, need to hold Britain to earlier commitments, such as its decision to send British personnel to train Ukrainian troops. “DOD will have to make sure we message to the U.K. that we want them to help us on items that are priority,” she said.

Officials acknowledge that the one area where the exit vote has the potential to drag on Britain’s military clout is defense spending. In 2014, the Cameron government committed to spending 2 percent of Britain’s gross domestic product on defense, making the U.K. one of only five NATO member states that did so in 2015.

Now, with its currency plummeting, its future trade ties up in the air, and its political landscape in disarray, Britain could well slip into recession, potentially shrinking defense spending along with economic activity.

That might also impact Britain’s ability to pursue expensive military technology. The British navy is preparing to launch an aircraft carrier that would eventually host U.S.-designed F-35 jets.

It’s too soon to tell how the post-exit realities for Britain will impact efforts to defend Europe from terrorist attacks like those in Paris and Brussels, or how it will shape officials’ willingness to commit troops and resources to far-away conflicts.

“There has always been this strain within the U.K., like in the U.S. and other places too . . . wariness about doing things overseas,” the U.S. official said. “After the Brexit I would hope that the government and the people will see how important it is that they continue.”

While last week’s vote was an expression of many Britons’ desire to put national interests first, American officials voiced cautious optimism that British leaders would uphold their tradition of employing military power, allowing the two countries’ battlefield partnerships to continue.