Chernobyl murdered during the Nazi occupation of 1941–44. Twenty years later, the area was chosen as the site of the first nuclear power station to be built on Ukrainian soil. The Duga over-the-horizon radar array, several miles outside of Chernobyl, was the origin of the Russian Woodpecker; it was designed as part of an anti-ballistic missile early warning radar network. With the dissolution of the Soviet Union in 1991, Chernobyl remained part of Ukraine. On 26 April 1986, Reactor No. 4 at the Chernobyl Nuclear Power Plant exploded after tests were done on the reactor improperly and the operators lost control.
Chernobyl Nuclear Power Plant was equipped with both types of turbines; Block 4 had the newer ones. The newer turbines, however, turned out to be more sensitive to their operating parameters, and their bearings had frequent problems with vibrations. Four RBMK reactors were at Chernobyl Nuclear Power Plant, Ns. 1–4. The construction of two partially completed reactors, numbers 5 and 6, was suspended immediately after the accident at reactor N. 4, and was eventually cancelled in 1989. Reactors 1-3 continued to operate after the disaster. Reactor N. 2 was permanently shut down in 1991 after a fire broke out due to a faulty switch