After the Second World War, another tide of the arms race slowly but surely began to develop in the world. With the first nuclear power plant built in Obninsk back in 1954, in the former Soviet Union, it became clear that atomic weapons and the nuclear industry overall would mark the second half of the twentieth century. Today, about 80 years after the first nuclear reactor ever built, "Chicago Pile-1", the current numbers for the commercial use of nuclear power indicate that 50 countries operate about 220 research reactors with as much more operating power plants in majority of these countries. The military numbers are expected to be even higher, and the fact is that nuclear submarines and ships can be equipped with multiple nuclear reactors on board. Some of the aircraft carriers can have up to eight of them.