Question: How many existing basic design types are there of the weapons the United States and the Soviet Union had an arms race over?

 During this period, in addition to the American and Soviet nuclear stockpiles, other countries developed nuclear weapons, though none engaged in warhead production on nearly the same scale as the two superpowers. The nuclear arms race was a competition for supremacy in nuclear warfare between the United States, the Soviet Union, and their respective allies during the Cold War. <SEP> At the conclusion of World War II the Allied nations began the process of disarmament of Axis controlled regions.  Japan occupied Korea at this time and had been in control since 1910.  In 1945, the decision was made to have American Marines forces oversee Japanese surrender and disarmament south of the 38th parallel and the Soviet Union would facilitate the change of power to the north.  At the time there was no political motivation and seemed to be a logical and convenient plan of action.  The original agreement and intent was to create a unified and independent Korea out of the post Japanese occupation era.  Instead each side of the 38th parallel established its own government under the influence of the occupational country; the United States in South Korea and the Soviet Union in North Korea.  Both new Korean governments discredited the other and claimed to be the only legitimate political system.  Tensions between the North and South escalated and each side began to petition foreign powers for resources and support.  South Korea wanted weapons and supplies from Truman and the United States government while North Korea sought help from Stalin and the Soviet Union.  The United States was still war weary from the disruptive World War II campaign and refused South Korea's request for weapons and troops.  North Korea convinced the Soviet Union to supply them with the weapons and support they requested.  This decision coincided with the United States withdrawing the last remaining combat troops from South Korea.  North Korea saw its opportunity and attacked South Korean forces at the 38th parallel on June 25, 1950 and thus initiating the Korean War. <SEP>  There are three existing basic design types.  In many existing designs, the explosive energy of deployed devices is derived primarily from nuclear fission, not fusion. Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate.  (This includes fission of any U-238 tamper or casing due to fusion produced neutrons.) <SEP> The Bomb is a 2015 American documentary film about the history of nuclear weapons, from theoretical scientific considerations at the very beginning, to their first use on August 6, 1945, to their global political implications in the present-day.  The two-hour PBS film was written and directed by Rushmore DeNooyer, who noted the project took a year and a half to complete, since much of the film footage and images was only recently declassified by the United States Department of Defense.  According to DeNooyer, “It wouldn’t take very many bombs to really change life on Earth, ... The idea that there are thousands of them sitting around is pretty scary.  I don’t think people today realize that.  They don’t think about it.  I don’t think they are scared.  But in a way, they should be.”  Mark Dawidziak, of the "Cleveland Plain Dealer", summarized the film as follows: ""The Bomb" moves swiftly to cover Hiroshima and Nagasaki, the Cold War, the arms race, the Red Scare, the witch hunt, the Cuban Missile Crisis, test-ban treaties, the "Star Wars" initiative, the anti-nuke movement, the collapse of the Soviet Union and the rise of new nuclear threats."  According to historian Richard Rhodes, “The invention [of 'The Bomb'] was a millennial change in human history: for the first time, we were now capable of our own destruction, as a species.”