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.
Their accuracy is especially vital now that the conflicts in Ukraine and the Middle East have revealed the potential for drones to be deployed as frontline weapons.
Poland last month signed a $1bn (£790m) deal with the US for four aerostats that will be used to scan its eastern border for missiles, aircraft, drones and seaborne incursions, and Mr Riksen said the remit of the TARS also includes the detection of potential hostile drone threats.
Diesel-powered blimps like those deployed by QinetiQ can stay aloft for as long as a week before they need refuelling, making them ideal for what’s known as persistent surveillance, though extreme weather can force them to be grounded.
Each balloon is moored with a nylon fibre cable, and raised and lowered with a powered winch. TARS operates from six sites along the US-Mexico border, one that scans the Florida Straits, and another in Puerto Rico, monitoring the north Caribbean area.
QinetiQ was created in 2001 out of the Defence Evaluation and Research Agency, Britain’s largest science and technology organisation and itself formed out of a number of government bodies that had their origins in the Cold War.
The firm’s name has been taken to be a reference to Q Branch, the fictional MI6 department tasked with developing spy gadgets and weapons in the James Bond films.
The company said in a trading update last month it had identified opportunities to grow the value of the five-year TARS contract by 50pc.