By the mid-1960s both sides had much more accurate understanding of the opposition's forces. While the Soviets were catching up to the Americans' strategic nuclear weapons, NATO was catching up to the Warsaw Pact's conventional forces, in part with tactical nuclear weapons. This increased both sides' confidence; a 1964 Warsaw Pact plan for Czechoslovakia written as a result of the Berlin Crisis of 1961 assumed that the East could capture Lyon within two weeks after the start of hostilities, while contemporary NATO plans expected that it could stop the Warsaw Pact near the eastern border of West Germany, in contrast to the earlier fears of the English Channel if at all. The Warsaw Pact plan did not consider the possibility that American strategic weapons might have crippled the Soviet Union, assuming that superior Soviet air defenses would have stopped most enemy missiles while invading NATO troops would have, the plan stated, "suffered enormous losses from nuclear strikes".