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Why are tests needed? Different tests have different purposes. Some are aimed at improving existing nuclear weapons. Designers need to know accurately how much smaller a weapon can be made without loss of punch, how much of a scarce ingredient can be safely omitted, or whether the weapon can be changed in shape to fit another warhead. Most of the answers can be worked out in theory on complex computers, but the history of weapons is full of embarrassing surprises, and scientists can never be sure until the modified weapon has been exploded and its performance has been measured. New and radical kinds of nuclear explosives need testing to see if they will explode at all, or if their performance will justify their cost and weight. Still other tests are merely experiments in nuclear physics. The device tested may be useless as a weapon, but scientists hope that its explosion will yield information about the behavior of atoms and subatomic particles which they cannot obtain in any other way. These far-out tests may be the most important of all because they lead to long-range progress.
What U.S. weapons have already been tested? At the start of the test moratorium in the fall of 1958, the U.S. had a family of well-tested bombs ranging in power from less than one kiloton (1,000 tons of TNT) up to 20 megatons (equivalent to 20 million tons of TNT). The 20-megaton weapons are too heavy for existing U.S. missiles, but more than one of them can be carried by far-ranging B-52 bombers. U.S. authorities, both civilian and military, see little advantage in more powerful bombs, such as the 100-megaton horror mentioned by Khrushchev, because the damage the monsters could do would not increase in proportion to their weight. At any rate, a single 20-megaton bomb is enough to destroy any modern city. In its present H-bomb arsenal, the U.S. has reliable 2-megaton warheads for the Titan I missile, and 500-kiloton warheads for the Navy's Polaris and the Air Force's Minuteman. In an age of megaton H-bombs, mere kilotons sound strangely small, but the Minuteman warhead explodes with 20 times the force of the primitive, 20-kiloton A-bomb that destroyed Hiroshima in 1945. killing 78,-ooo people. Ranging down in power, the U.S. has a large group of small tactical nuclear weapons for use in light rockets, artillery shells, torpedoes, antisubmarine depth charges, air-to-air missiles, etc. The warhead of the air-to-air Genie, which is carried by interceptor planes, yields one-tenth kiloton (100 tons). The state of the stockpile of these weapons is secret, but no U.S. authority can be found who does not believe that the U.S. is far ahead of the Russians in both quantity and quality of nuclear explosives. It is agreed, also, that both countries have more than enough weapons on the shelf to devastate each other—and to kill much of the hu man race as well. A great deal of the destruction would be the result of radio -active fallout.
What remains to be tested? In spite of the stockpiled ability to overkill, testing is still profitable. All experts believe that nuclear explosives can be "improved" —made deadlier and more precise—by slow refinement and by large technical breakthroughs. Explosive efficiencies are still far below the theoretical maximums.