Hundreds of Ukrainian kamikaze drones have flown towards Moscow in recent weeks. None appear to have even reached the Russian capital, yet the effect on the city — and the wider country — has been hugely significant.

The covert operation was described as one for the “history books” by Ukraine’s president. According to Ukrainian officials, nearly a third of Moscow’s strategic bomber fleet was destroyed or damaged with cheaply made drones sneaked into Russian territory in the span of a few hours on Sunday.

The audacious attacks on Russian airfields highlight the power of unconventional, asymmetric warfare — and the threat to U.S. strategic bases and ports, experts say.