Spanning 700 metres (2,300 ft) in length and 150 metres (490 ft) in height, the Duga (Russian: Дуга́, lit. ‘arc’ or ‘curve’) was an over-the-horizon system used in the Soviet Union as part of its early-warning radar network for missile defense.

The duga system was extremely powerful, reaching over 10 MW, and emitted in the shortwave radio bands. It was given the nickname Russian Woodpecker by shortwave listeners for its emissions randomly appearing and sounding like sharp, repetitive tapping noises at a frequency of 10 Hz.