generate questions: The most extreme case was the Soviet Union, and this model may still be followed in some countries: it was a separate service, on a par with the navy or ground force. In the Soviet Union this was called Voyska PVO, and had both fighter aircraft and ground-based systems. This was divided into two arms, PVO Strany, the Strategic Air defence Service responsible for Air Defence of the Homeland, created in 1941 and becoming an independent service in 1954, and PVO SV, Air Defence of the Ground Forces. Subsequently these became part of the air force and ground forces respectively
Which country had the most severe case? {sep_token} This separate service  was known as what in the Soviet Union? {sep_token} What two systems did Voyska PVO have? {sep_token} What year did the PVO Strany become independent? {sep_token} What was the arm that was the Air Defence of the Ground Forces?