Ukraine is celebrating its independence day on Sunday, which marks the country's declaration of independence from the Soviet Union in 1991. The UK government has announced that Ukrainian flags will appear above Downing Street on Sunday in recognition of the anniversary.

Many of the drones aren’t particularly fast or high-tech, but they are cheap enough for the Kremlin to launch more than 700 in one night, in an effort to overwhelm Ukraine’s air defenses. Here’s what we know.