The drone strikes on Russian air force bases weaken Moscow’s ability to wage war on its neighbor and undermine its capacity to threaten more distant rivals.

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.

After more than three years of war, Moscow and Kyiv are engaged in direct discussions to end the fighting, but their positions remain far apart.