GATWICK, ENGLAND — The second-busiest airport in the United Kingdom was recently beset by a robotic menace. Starting at 9 p.m. GMT Dec. 19, a pair of drones was spotted near the airport, prompting the airport to cancel flights until 6 a.m. Friday. Airlines scrambled responses, passengers remained delayed and confused as their holiday travel plans were increasingly sent out of whack, while Sussex police actively searched for the people at fault.

The military has been called in for assistance with counterdrone equipment, as the rest of the world ponders two similar, related questions: How can drone flybys cause so much disruption, and why isn’t there a tool that can stop them yet?

“Drone” is an expansive category, which has swallowed everything from military-specific aerial targets and high-altitude remotely operated observation platforms to everything flying and without a human on board, including toys as well as somewhat more capable tools priced at a few hundred dollars. That latter category makes up a massive expansion in the number of objects controlled by humans that can be put into the air. In January 2018, the UK had registered roughly 20,000 people-carrying aircraft, in every category from gas-filled airships to fixed-wing planes to gliders. A 2014 estimate prepared for the House of Commons put the number of drones purchased in the United Kingdom at over 530,000.

More drones would naturally lead to more drone sightings, but what stands out at Gatwick is the proximity of those drone sightings to the airport. Keeping those drones away is primarily the function of law, with private drone flights prohibited within 1 km (3,280 feet) of an airport boundary, and with drone flights restricted to below 122m (400 feet) in altitude. (In the United States, the FAA recommends that drone pilots only fly within 5 miles of an airport of helipad if they have notified air traffic control.) Some drone companies, like China’s massive DJI, program geofences into the drones they sell, which prevent drones from flying within certain GPS coordinates, like the area around airports.

If someone wants to avoid geofencing, there are ways to modify the drone that evade the restrictions. In response to what appeared to be footage of a DJI drone dropping bombs in the fighting in Ukraine, DJI issued a statement that geofencing is intended for people who want to follow the law, “and is not designed to defeat people who are consciously trying to do ill.”

The persistence of the drone flights near Gatwick, and the possible use of multiple drones, suggest that this is more malicious than a simple accident caused by someone who doesn’t understand where, exactly, they aren’t supposed to fly a drone. If it is a malicious use of a drone, or multiple drones, what tools are available to stop it?

The counterdrone world — as a natural response to the drone market and in particular an adaption to the use of cheap commercial drones as weapons in Iraq, Syria and Ukraine — offers a multitude of potential remedies. The most comprehensive market survey, assembled by the Center for the Study of the Drone at Bard College in February 2018, listed 235 different counterdrone offerings. Those counterdrone mechanisms included everything from eagles to lasers, and from detection machines to interdiction tools.

As a young, unsettled market, there’s not a clear singular answer, but many of the approaches focused are on hand-held or fixed-installation jammers, which point a directional antenna at a drone and try to disrupt the signal it receives from its controller. These devices, especially the handheld point-and-signal antennas, have seen use in Afghanistan and Iraq, but they have severe restrictions in exactly how effective they are.

One limitation is that the person wielding the drone-jamming antenna has to continuously train the antenna on the drone, to keep it within a cone where the electromagnetic interference is effective. The second is that these jammers are one-to-one with the drones they jam, so multiple drones require multiple jammers. Finally, there is the matter of range. The DroneKiller jammer, for example, claims a detection of two miles but a jamming range of only 1,300 feet, or less than 400m. Getting coverage around an airport with individual jamming rifles is labor-intensive, at best, and the jammer-rifles do not come cheap. The drone-killer is priced at around $30,000.

As drone sightings plagued Gatwick, Gavin Williamson, secretary of state for defence and MP for South Staffordshire, said that the military would be providing unique capabilities to the airport, but declined to specify what those capabilities are. It is possible that it includes jamming and detection tools. Few tools on the market are listed as specifically capable against multiple drones and of those that are, the Center for the Study of the Drone knows of no independent verification to support the claim.

Countering multiple new aircraft at once is a novel problem. While the history of anti-air weapons is largely a history of matching a specific weapon to a single target, the Flak cannons of World War II had the reach and power to disrupt and destroy dense formations of planes by hurling a cloud of painful shrapnel into the sky. Adopting that approach for formations of miniature airborne robots has yet to attract any serious attention in a military application. It is deeply unlikely it would find a home in civilian counterdrone efforts.

The closest to a kinetic, shooty solution may be the most straightforward: bullets. The authority to shoot down drones with guns is one the Department of Homeland Security asked for in July 2018. It is an option law enforcement is open to in Gatwick, as the drone buzzing the airport continues into its second day. As security forces around the world look to Gatwick as an example of the disruption that even a drone flight can cause, and start to worry about gimmick drones in terrorism, it is increasingly likely that the most immediate counterdrone tool will be guns already on hand. Where the fired bullets land will remain an afterthought.