On May 31, 1945, sixteen men met in the office of Secretary of War Henry L. Stimson. The sixteen men were there to make decisions about a weapon the average American had never heard of--the atom bomb. They picked future targets for "The Bomb." They were not talking about "just another weapon." What they were discussing was "a new relationship of man to the universe," as said by Stimson. Humankind, the Secretary seemed to be saying, was at the most critical turning point in its entire recorded history.

There was, however, a more "practical" part of the agenda. The supersecret group also had many questions about the future including:

• What were the chances of producing nuclear weapons more powerful that the one being developed?
• How long would it take other nations, especially the Soviet Union, to catch up with the United States?
• What hope was there to use atomic energy for peaceful purposes, such generating as electricity?

The Origin and Development of Nuclear Weapons

It all started rather innocently in 1896, when Antoine Henri Becquerel discovered radioactivity in uranium. Becquerel, of course, did not envision the atom bomb when he made his discovery. The next step came in 1902 when Marie and Pierre Curie isolated a radioactive metal called radium. Three years later came an electrifying breakthrough, when Albert Einstein published his theory of relativity. Einstein asserted that matter (mass) and energy were two forms of the same thing. According to Einstein, if somehow we could transform mass into energy, it would be possible to "liberate" huge amounts of energy.

It was one thing to say this is theory, but it was another thing to do it. During the next decade, a major step was taken in that direction when Ernest Rutherford and Niels Bohr described the structure of an atom more precisely. It was made up, they said, of a positively charged core, the nucleus, and of negatively charged electrons that revolved around the nucleus. It was the nucleus, scientists concluded, that had to be broken or "exploded" if atomic energy was to be liberated.

In 1934, Enrico Fermi of Italy disintegrated heavy atoms by spraying them with neutrons. However he didn't realize that he had achieved nuclear fission. In December 1938, though, Otto Hahn and Fritz Strassman in Berlin did a similar experiment with uranium and were able to verify a world-shaking achievement. They had split an atom. They had produced nuclear fission. They had transformed mass into energy--33 years after Einstein said it could be done.

And on August 2, 1939, Albert Einstein wrote a letter to the American President, Franklin D. Roosevelt. "In the course of the last four months, he said, "it has been made probable--through the work of Joliot in France as well as Fermi and Szilard in America--that it may become possible to set up nuclear chain reactions in a large mass of uranium... This new phenomenon would also lead to the construction of bombs... A single bomb of this type, carried by boat or exploded in a port, might very well destroy the whole port together with some of the surrounding territory." He urged Roosevelt to begin a nuclear program without delay. In later years Einstein deplored the role he had played in the development of such a destructive weapon: "I made one great mistake in my life," he told Linus Pauling, another prominent scientist, "when I signed the letter to President Roosevelt recommending that atoms bombs be made."

So the development of the bomb continued. And on August 6, 1945, the Enola Gay, an American airplane, dropped the first atomic bomb ever used in warfare on Hiroshima, Japan, eventually killing over 140,000 people. On August 9, 1945, the United States dropped a second atomic bomb, this time on the Japanese city of Nagasaki. The drop is one mile off target, but it kills 75,000 people.

In the 19th century, the rapid advance of modern technology and industrial organization greatly increased both the destructive power of armed forces and the capacity of societies both to resist and to recover from an attack. Nuclear weapons carry the possibilities of destruction to a new level and are able to inflict far greater damage within a few hours than previously resulted from years of warfare. This not only makes the consequences of war worse but also raises new concerns about controlling such a destructive process. Indeed, nuclear weapons have not been used in war since the first two atomic bombs were dropped on Japan in 1945, but many countries, including many Third World countries, now have nuclear weapons.

The Main Types of Nuclear Weapons

The Ranges of Weapons

Ever since 1945 when the only two nuclear weapons ever used in war were dropped on Japan, the size, variety, and number of nuclear weapons have multiplied many times. In addition to free-falling bombs, there are now two main types of missiles:

• Ballistic missles follow a ballistic, or unguided, trajectory like an artillery shell after the powered boost phase. These missiles may undergo later minor corrections in mind-course or during reentry from space.
• Cruise missiles fly like small aircraft and may take a preset but devious course to the target at low altitude. In principle, either of these missiles can be launched from underground launch-tubes, or from submarines, surface ships, or aircraft.

Over the years, the accuracy of all delivery missiles has greatly improved. This does much more than increase the explosive power. A missile's measure of accuracy is its Circular Error Probable (CEP), which is the radius of the circle within which 50 percent of the shots are expected to fall. In today's most advanced systems, this error can now be reduced to about 50 feet! Nuclear weapons are also classified according to their range. Usually, weapons with a range of more than 3,000 miles are classed as intercontinental, or Intercontinental Ballistic Missiles (ICBMs). Weapons of between 600 and 3,000 miles are classed as Intermediate Ballistic Missiles (IRBMs). Weapons of intermediate range are on submarines (Submarine Launched Ballistic Missiles, or SLBMs) or on aircraft (Air Launched Ballistic Missiles, or ALCMs) are usually classed with the intercontinental weapons as strategic. Finally, weapons of up to 600 miles are usually classed as tactical, or shortrange, weapons.

In this page, missiles will be described in the following three categories:

• Land-based Missiles
• Air-to-Surface Missiles and Bombers
• Sea-launched Missiles

Land-based Missiles

The most common delivery system for nuclear weapons today is the ballistic missile, a rocket that follows a pre-set trajectory, or course, to its target. While earlier missiles had to be fueled just hours before launching, rockets today are powered either by liquid fuels that can be stored in the rocket or by solid fuels, and they can be launched in the few minutes it takes to set the course and open the doors of the missile tube, or silo.

A typical missile leaves its silo and climbs with energy from several stages of rocket fuel, discarding empty fuel casings for three or four minutes until reaching its cruising speed. After this boost phase, the warhead cruises through space for some 15 to 20 minutes, leaving the atmosphere. If it has multiple warheads that are destined for several targets, a carrier maneuvered by small rocket jets releases each missile on its own ballistic course. Along with the warheads may go lightweight false decoy warheads or chaff (radar-reflective strips) to confuse any defenses. Finally, the reentry period of two to three minutes occurs when the missile reenters the atmosphere.

Land-based missiles are often less vulnerable because they are mobile--or at least movable--and are mounted on transporters and accompanied by firing and control facilities. The most famous example of this missile is the Soviet SS20.

Air-to-Surface Missiles and Bombers

Manned bombers are the oldest type of vehicle used for modern strategic bombing missions. They possess the advantages of a high payload (lots of weapons), good control, and if they survive a mission, reusability. Offsetting these advantages is the greatly improved performance of modern air defenses, which is due to up-to-date surveillance techniques and effective antiaircraft missiles and interceptors.

There are several approaches a bomber can take to penetrate a defense. One is a change in tactics. For instance, aircraft today usually attack at very low altitude in order to avoid detection and prolonged visibility to defenses. But this is expensive in fuel use and puts great strain on the crew and on the aircraft. An alternative is to equip the craft with ballistic or cruise standoff missiles to fly the final stages. The third approach to penetration has generated lots of excitement. It involves making the aircraft or cruise missile less visible to detection. Very modern and still high secret stealth techniques, such as the following

• reshaping the vehicle to reduce radar echoes,
• suppressing heat sources that are vulnerable to infrared detection,
• using radar-absorbent materials and paint, and
• equiping the vehicle with active and passive electronic devices to suppress or distort radar images

have shown great promise. They have given new life to bombers and other aircraft once thought to be on the verge of obsolescence and have greatly improved the penetration capability of the small cruise missiles.

Sea-Launched Missiles

The vulnerability of missiles to attack before launching led to building hardened silos for ICBMs. Another solution has been to put missiles in nuclear propelled submarines. These submarines are very difficult to detect, especially when they are able to cruise for weeks without surfacing. Today some 200 ballistic missile submarines are in the US, Russian, British, French, and Chinese forces, which have stimulated great efforts in antisubmarine warfare.

Submarine-Launched Ballistic Missiles (SLBMs) used to be inaccurate because the submarine, forced to remain below the surface, found it difficult to identify its exact position, and therefore, could not set an accurate course for the missile. Modern navigation devices and the possibility of building corrective guidance systems into the reentry vehicles themselves have greatly improved performance in this respect, however. As a result, the SLBM is the supreme example of a retaliatory nuclear weapon that is capable of "riding out" an attack and remaining ready to retaliate. This makes the SLBM system very attractive to small nuclear powers such as Britain and France who have to rely on very few weapons.

So far, the SLBM has seemed to be the indisputable last resort against the loss of retaliatory forces to enemy attack. An approach to reducing possible costs has been to build larger submarines that can carry more missiles. There is a Russian submarine, for example, that carries 20 missiles with multiple warheads. With more eggs in fewer baskets, new vulnerabilities in anti-Submarine Warfare are inevitable.

The Atom Bomb

The atomic bomb works by a physical phenomenon known as fission. In this case, particles, specifically nuclei, are split and great amounts of energy are released. This energy is expelled explosively and violently in the atomic bomb. The massive power behind the reaction in an atomic bomb arises from the forces that hold the atom together called the strong nuclear force. The element used in atomic bombs is Uranium-235. Uranium's atoms are unusually large, and henceforth, it is hard for them to hold together firmly. This makes Uranium-235 an exceptional candidate for nuclear fission. Uranium is a heavy metal and has many more neutrons than protons. This does not enhance their capacity to split, but it does have an important bearing on their capactiy to facilitate an explosion.

When a U-235 atom splits, it gives off energy in the form of heat and Gamma radiation, which is the most powerful form of radioactivity and the most lethal. When this reaction occurs, the split atom will also give off two or three of its "spare" neutrons, which are not needed to make either of the parts after splitting. These spare neutrons fly out with sufficient force to split other atoms they come in contact with. In theory, it is necessary to split only one U-235 atom, and the neutrons from this will split other atoms, which will split more...so on and so forth. This progression does not take place arithmetically, but geometrically. All of this will happen within a millionth of a second.

Uranium is not the only material used for making atomic bombs. Another material is the element Plutonium, in its isotope Pu-239. However, Plutonium will not start a fast chain reaction by itself. The material is not fissionable in and of itself, but may act as a catalyst to the greater reaction. The bomb basically works with a detonating head starting off the explosive chain reaction.

The Hydrogen Bomb

The Hydrogen bomb works on a different physical principle known as nuclear fusion. In nuclear fusion, the nuclei of atoms join together, or fuse to form a heavier nucleus. This happens only under very hot conditions. The explosion of an atomic bomb attached to a hydrogen bomb provides the heat to start fusion. Hydrogen nuclei fuse to form helium and as this happens, huge amounts of energy are released from the hydrogen nuclei, producing a huge explosion.

Fusion releases energy due to the overall loss in mass. If you add up the masses of the particles which go into a fusion reaction, and you add up the masses of the particles which come out, there is frequently a difference. According to Einstein's famous law relating energy and mass,

,

the "mass difference" can take the form of energy. Fusion reactions involving nuclei lighter than iron typically release energy, but fusion reactions involving nuclei heavier than iron typically absorb energy. The amount of energy released depends on the specifics of the reaction. The reaction used in the hydrogen bomb, though, produces one of the greatest changes in mass.

The hydrogen bomb is thousands of times more powerful than an atomic bomb. There have not been any hydrogen bombs used in warfare, however there have been hydrogen bomb tests. Most of these tests are done underwater due to risk of destruction. To give you an idea of how strong the H-bomb is, think about this. This atomic bomb dropped on Hiroshima, Japan which killed over 140,000 people had the power of 13 kilotons. A common hydrogen bomb has the power of up to 10 megatons. All the explosions in World War II totalled "only" 2 megatons -- 20%  of the power of ONE common hydrogen bomb.

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