The Don-2N radar (Russian: Дон-2Н, NATO: Pill Box) is a large missile defence and early warning radar outside Moscow, and a key part of the Russian A-135 anti-ballistic missile system designed for the defence of the capital against ballistic missiles. Located in the Pushkino district of Moscow it is a quadrangular truncated pyramid 33 metres (108 ft) tall with sides 130 metres (427 ft) long at the bottom, and 90 metres (295 ft) long at the top. Each of its four faces has an 18 metres (59 ft) diameter UHF band radar giving 360 degree coverage. The system is run by an Elbrus-2 (Russian: Эльбрус-2) supercomputer.
Under the 1972 Anti-Ballistic Missile Treaty both the United States and the Soviet Union had to designate one area to protect from missile attack. The USA chose North Dakota and the Soviet Union chose Moscow. The Don-2N radar is designed to be the control centre of the system and can operate autonomously if connection is lost to its command and control centre.