A defence firm dubbed Britain’s real-life Q-branch has taken a key role in America’s war on drugs, deploying a fleet of radar-equipped blimps that scan for border incursions.

QinetiQ, the FTSE 250 defence company, is managing the airship-like craft which is deployed at intervals along the 2,000 mile stretch between Arizona and Florida.

The blimps can ascend to altitudes of up to 15,000 feet, with a viewing range of 200 miles allowing them to more easily spot the low flying planes and speed boats favoured by drug runners.

QinetiQ was awarded the $170m (￡133m) Tethered Aerostat Radar System (TARS) contract by the US Department of Homeland Security last November, taking over responsibility for the network of eight blimps and ground stations and more than 200 employees.

The TARS fleet was first deployed in the 1980s, when drugs and contraband were typically carried aboard planes landing on dirt runways in an estimated 8,500 illegal flights a year.

More than 500 aircraft were seized by Mexican authorities from drug kingpin Joaquin “El Chappo” Guzman alone, most of them innocuous looking Cessna aircraft, popular because they could operate from a 900-foot airstrip and featured double doors for quick unloading.

The TARS balloons, known as aerostats, helped US officers intercept planes or boats illicitly entering US territory and to anticipate where gangs might cross the border from planes landing on makeshift runways still inside Mexico.

Today, flows of cocaine, heroin, marijuana and methamphetamine have been joined by fentanyl, the synthetic opioid 100 times more potent than morphine that’s spawned a new US drugs crisis, with more than 70,000 overdose deaths reported in 2022.

The Drug Enforcement Administration last year seized a record 79.5 million fentanyl pills and more than five tons of fentanyl powder.

The task facing QinetiQ and the air and marine arm of Customs and Border Protection, which operates the aerostats, has become even more demanding with the advent of cheap but durable drones.

Jonathan Riksen, executive vice president at QinetiQ, said: “A drone is obviously much smaller than an aircraft. That’s problematic because not only is it harder to detect, but it can look like a goose or some other larger bird in terms of its radar returns.”

High-altitude radars are far more effective in identifying targets because they render the background flat, Mr Riksen said, whereas ground-based scans can suffer distortion when an object is viewed against a mountainside or forest.

So acute are the TARS radars that they can even spot a drone’s spinning blades, he said.