U.S. special operations unit to buy passive drone sensors for UK base

The U.S. Air Force wants to install a network of microphones at one of its most secretive bases in England, built specifically to hear enemy drones coming before anyone ever sees them.

A newly published Air Force solicitation reveals that the 352nd Special Operations Wing at RAF Mildenhall is seeking a passive acoustic drone detection system, a network of sensors that listens for the distinctive sound signature of small unmanned aircraft rather than emitting any radar or radio signal that could reveal the system’s own location to an adversary scanning for exactly that kind of transmission.

The solicitation names Squarehead Technology’s Discovair array G2+ as the preferred system, though it allows competing vendors to bid an equivalent product, and specifies that the Air Force wants four networked sensor units capable of detecting and classifying both Group 1 and Group 2 drones, the two smallest categories in the military’s five-tier classification system covering everything from tiny commercial-style quadcopters up to slightly larger recreational aircraft weighing up to 55 pounds (25 kilograms).

Each individual sensor must detect a Group 1 drone, the kind of consumer quadcopter sold under brands like DJI’s Mavic line, from at least 500 meters (1,640 feet) away under optimal conditions, while covering a minimum field of view of 100 degrees in both horizontal and vertical directions, wide enough that a handful of networked units can realistically cover an entire base perimeter without leaving obvious gaps in coverage.

RAF Mildenhall serves as the headquarters for the 352nd Special Operations Wing, the only Air Force special operations unit assigned to the European theater, home to CV-22 Osprey tiltrotor aircraft and MC-130J Commando II transport planes that support classified special operations missions across Europe, Africa, and parts of the Middle East. Unauthorized drones swarmed over Mildenhall and two neighboring bases, RAF Lakenheath and RAF Feltwell, for several consecutive nights starting November 20, 2024, with U.S. officials confirming at the time that groups of up to 20 drones at once appeared in restricted airspace, forcing inbound aircraft to divert and prompting Britain to deploy roughly 60 combat troops to help defend the installations. The drones later spread even further, appearing over RAF Fairford in Gloucestershire, more than 130 miles (209 kilometers) from Mildenhall, where four American B-52 bombers were deployed at the time as part of a rotational bomber task force.

Britain’s Daily Mail reported in November 2025, citing documents obtained under the country’s Freedom of Information Act, that police logs from the original incident described a National Police Air Service helicopter forced into an emergency evasive dive after two fast-moving objects appeared to pursue and match speeds with the aircraft at roughly 140 knots (161 miles per hour or 259 kilometers per hour), a far more alarming account than the version originally given to the public. Those same police logs recorded witnesses describing swarms of 10 to 15 drones potentially entering base airspace across a three-day window, details that had not been previously disclosed and that only came to light through the records request nearly a year after the original incursions.

Against that backdrop, a passive acoustic detection system offers a specific tactical advantage that traditional radar-based counter-drone systems cannot match. Radar works by actively broadcasting a signal and listening for the reflection bouncing back off a target, a method that reliably detects larger aircraft but often struggles against small, slow-moving drones built from materials that return a weak radar signature, and radar transmissions themselves can reveal a defended site’s exact location and capabilities to anyone monitoring the electromagnetic spectrum nearby.

A passive acoustic array sidesteps both problems entirely, listening only for the sound of a drone’s motors and propellers without ever emitting a detectable signal of its own, and the Air Force’s technical requirements specifically call for a system that keeps working even in environments where GPS signals are jammed, degraded, or entirely denied, exactly the kind of contested electromagnetic conditions a real adversary would likely create before attempting another incursion.

The solicitation requires every sensor to be man-portable, weighing no more than 10 kilograms (22 pounds) per unit, letting a single Airman deploy the system quickly in either a fixed installation or an expeditionary environment without needing specialized lifting equipment. Bidders have until August 4, 2026, to submit quotes to the 48th Contracting Squadron, though the solicitation notes plainly that funding for the effort is not yet available and no contract award will follow until money is actually appropriated, a standard caveat that nonetheless underscores how much of this procurement remains contingent on budget decisions still working their way through the system.