Why are there so many security incidents linked to US military in Britain?

A string of recent security incidents at UK military bases used by the United States have forced Washington to hastily relocate several of its aircraft and upgrade the threat level facing some of its troops. On two occasions, once in October and once in November, the US has moved aircraft following threats that officials said emanated from Iran. And in a separate October incident, two Latvian men were arrested inside another Royal Air Force (RAF) base used by US personnel.

The frequency of the incidents indicates both the risks inherent in the United Kingdom’s decision to allow US forces to launch defensive strikes against Iran from its airbases, and the country’s strategic significance as a host for expensive US aircraft that make for attractive targets. Britain’s government insists its bases remain secure and says it has heightened security measures across its sites. So, how unusual are these incidents, and why do they seem to be concentrated in the UK?

Are there more US troops in the UK than elsewhere? No. About 12,300 US military and defense personnel are stationed in the UK, according to the British government in March, but far more are based in Germany where the US European Command is headquartered. Italy hosts about the same number of American troops as the UK. How important are UK bases to the US military? The UK may not have the highest number of American troops stationed on its soil, but its bases are of enormous strategic importance, often hosting extremely expensive US aircraft.

RAF Mildenhall is the US’ only permanent home in Europe for its refueling aircraft, providing critical support that allows US forces to deploy quickly anywhere in the world. Flight tracking data analyzed by CNN shows that 10 US refueling aircraft were relocated away from the base on Monday following a threat from Iran that was deemed credible, according to a person familiar with the intelligence which prompted the evacuation. The source declined to detail the nature of the threat to the base but said that the US intelligence community has in recent weeks picked up a wide range of “varied, extensive, and specific” plots being discussed by the Iranians against American targets.

RAF Fairford, which was targeted in September, holds similar strategic significance. Its long runway means it is one of the few US bases in Europe capable of handling all three types of long-range bombers operated by the US Air Force. Importantly, the US has used Fairford to carry out strikes on Iranian missile sites used to attack ships in the Strait of Hormuz, meaning that US B-1 bombers have been stationed there. That made it a prime target for the failed plot, which was directed by the commander of an Iranian terrorist proxy group from his imprisonment in New York, US federal prosecutors alleged in a new indictment on Tuesday.

The plan involved using vans filled with fuel as vehicle-borne improvised explosive devices, multiple people briefed on the matter told CNN. As well as targeting US assets, another key aim for Iran in its external attacks has always been to weaken relationships among the US and its allies, said Louise Kettle, a professor at Nottingham University who studies British-Iranian relations. In these cases, “it is about weakening relationships between the US, the UK and Israel,” she told CNN.

Are security threats in Britain more acute? In the months after the US and Israel first launched strikes against Iran, the threat the Islamic Republic poses to the UK has shifted. It has attempted to expand its hybrid operations and altered its strategy to “come at harder targets, like military sites,” according to MI5 chief Ken McCallum. That mirrors a wider change in Iran’s strategic approach as its traditional policy of maintaining a “forward defense pattern” through its proxy groups across the Middle East has crumbled, Kettle said.

“Not only has the UK changed its approach by allowing the US to use the bases, not only has the global context changed because the US is at war with Iran, but Iran’s strategic capabilities have also changed, and therefore you must expect them to change their strategy,” she added. Just last week, Iranian state-linked media Hamshahri threatened other European bases, including some situated in Germany, Italy and Greece. “We’ll see what happens,” the newspaper’s front page warned, complete with a mocked-up map of Europe and red pins marking each base it threatened.

McCallum said the Fairford incident was “not unique,” adding that “there have been other examples, not just in the UK, but around the world,” without providing further details. Still, McCallum noted that Iran’s capabilities when operating far outside its borders are mostly limited to subcontracting “criminal proxies.” That limits its capabilities to only the “sophistication level of those criminals,” he added, saying that the police and intelligence services can currently deal with these threats “pretty capably.”

In the UK, the threats have primarily manifested as attacks on the Jewish community, dissident journalists and against military bases. But they can take different forms in different countries. France, which has no permanent US troops to target but took part in “defensive” operations against Iran, blamed the Islamic Revolutionary Guards Corps on Monday for last month’s supermarket fridge cyberattack that spoiled produce at around 700 retailers, a claim Tehran says is “baseless and hostile.”

How unusual are these types of incidents? When British police were alerted to three suspicious vehicles driving toward Fairford in September, the incident sparked huge international attention for its unusualness. But military bases, by their very nature, are always targets for an attack. “If you host another country who are fighting someone else, (bases) naturally becomes a target for the country they are fighting,” noted Kettle. “So, this isn’t unique to the UK, it’s a standard part of warfare.”

Back in November 2024, several bases across Europe which host US troops reported seeing small drones flying over them. They were never officially identified but a report from the International Institute of Strategic Studies, a security think-tank, assessed they could have been part of a campaign directed by Moscow. Security at British bases is “layered and intelligence-led,” the country’s minister for defense readiness, Luke Pollard, said Thursday.

“It combines physical protection, access controls, surveillance, policing, guarding, aerial monitoring, and counter-drone capabilities. We do not rely on any one single measure.”