The drones that exploded over the Kremlin this week likely evaded air defense systems in and around Moscow, suggesting thatThey may have been launched from Russian territoryaccording American experts.

After the release of drone videos, governments and intelligence analysts are scrambling to discover the origins of the drones, which are designed to fly to a predetermined destination and explode. Moscow had been working to protect the Kremlin from drones since at least 2015, when it began using electronic countermeasures to drive away such drones by spoofing their geo-location signals, explained Dana Goward, the president of the non-governmental organization nonprofit Resilient Navigation and Timing Foundation, which advocates for a more robust and widespread GPS system.

This spoofing occurs when a fake GPS signal is sent to replace a normal one, misleading the direction systems of drones or other devices.

Goward said sophisticated Russian defense systems may suggest that the drones that reached the Kremlin, which he believed to be of medium size, “were probably not using GPS but were manual – meaning they were launched from close range – or just following a predetermined course, kamikaze style’.

Two of the many videos posted on Russian social media sites show two objects flying on the same course towards the Senate dome, one of the highest points of the Kremlin complex. The first is destroyed leaving only a little smoke behind, while from the second burning debris can be seen falling into the dome.

Russia accused Ukraine of orchestrating the attack with US help. Kiev and Washington deny any involvement.

How did they get to the Kremlin?

“It is surprising that this drone managed to fly all over Moscow, all the way to the Kremlin, without being detected and destroyed,” said Blake Resnick, the founder and CEO of drone maker BRINC. “The relatively small size and low height may have helped. If the drone didn’t use GPS and communicate with a ground control station, that would also make it difficult to jam (its signal) or spoof,” explained.

According to Goward, the Kremlin has some defense systems that rely on radar and visual tracking and use bullets or explosive projectiles to protect the compound from drones or even missiles.

According to Dan Goettinger of the Vertical Flight Society, the drone used in the Kremlin appears to be a fixed-wing unmanned aerial vehicle, one of the largest offensive drones of its kind already in use or under development. Few countries have military-type kamikaze drones with the ability to cover longer distances – for example, to fly from Ukraine. About six larger military aircraft in use or under development have the ability to fly 400-plus kilometers. China, India, Taiwan and Ukraine are among the countries producing drones of such size and capabilities, Goettinger said.