actually flown from the roofs of large post offices. Several air forces adopted them, and the Soviet Union’s autogyros strafed the German invaders during World War II.
While de Cierva was working on his autogyro, an Argentine, Marquis de Petraras Pescara, invented cyclic pitch control on a helicopter with powered rotors spinning around a tilting rotor head, which made possible a practical helicopter. That was in 1924 — 21 years after the Wright brothers’ flight, which made possible a practical airplane. From there, progress was rapid. In 1936, Heinrich Focke of Germany produced a twin rotor helicopter that flew successfully. Two years later, it traveled 143 miles, reached a speed of 76 miles per hour and climbed to 11,243 feet.
Also in 1938, a Russian immigrant, Igor Sikorsky, who had earlier designed and flown groundbreaking large passenger and military planes in Russia, settled in the United States and started designing helicopters. In 1941, his single rotor ’copter smashed all records and became the basis of all modern helicopters.
The Germans had a few helicopters in World War II, but too few to accomplish anything noteworthy. In the Korean War, the small helicopters of the time were used extensively for reconnaissance, transporting generals, and, especially, evacuating wounded. Almost 80 percent of all the wounded airlifted to field hospitals got there by helicopter. Helicopters grew in size during that war, and in the next war, Vietnam, they were big enough to carry significant numbers of troops and artillery. They were used for reconnaissance; directing battles from the air; and taking part in battles with machine guns, automatic cannons, and rockets. They were still used for medical evacuation, and were the basis for all the tactics of the First Cavalry Division, the U.S. Army’s first “air mobile” division.
A deal between the U.S. Army and the U.S. Air Force gave all fixed-wing planes to the Air Force and all helicopters to the Army. Today, every U.S.
Army division includes helicopters. Helicopters have replaced all airborne divisions’ gliders and usurped most of the functions of their parachutes. Equipped with the wire-guided TOW rockets, they fight tanks; with the six- barreled modern Gatling guns, they mow down infantry; with other special equipment, they lay mines. In Iraq, they have taken part in street fighting. In Israel, and to a lesser extent in Iraq, they have been used to assassinate suspected terrorists.
Most helicopter successes have been against foes lacking effective antiaircraft fire. Even in Vietnam, where neither the Viet Cong nor the North Vietnamese Army was strong in antiaircraft weapons, helicopter losses were heavy.
A weapon like the Carl Gustaf recoilless gun (see Chapter 44) would be deadly against a hovering helicopter. A shell from a recoilless gun has far more velocity than a rocket, especially one of the guided rockets now used for antitank work. The chances of the helicopter evading the shot after it’s been fired are virtually nil.
Nevertheless, the “chopper’s” ability to take off and land on a postage stamp, to hover at will, to hide behind hills and other terrain features, to climb beyond the range of most ground fire, and to travel faster than any other vehicle except an airplane insures that it will continue to influence warfare for a long time.
Chapter 49
The Ultimate Weapon? Nuclear Weapons
At 8:15 a.m. on August 6, 1945, an American B 29 bomber flew over the city of Hiroshima, Japan and released something on a parachute. Hiroshima was a medium-size city, largely untouched by the war because it contained no military objectives worth touching. The object floating earthward under the parachute was the first nuclear weapon to be used in war. When the bomber was far away, but the parachute still above the ground, the bomb exploded.
Between 70,000 and 80,000 people in the city below died instantly or almost instantly. As many as 125,000 more died later as a result of injuries incurred by the blast. Three days later, a similar bomb exploded over Nagasaki, killing from 40,000 to 70,000 more people at once and 50,000 to 100,000 later from radiation sickness, cancer, or other illnesses caused by the explosion. Six days later, Japan surrendered.
The possibility of nuclear weapons had been known in the scientific community for years. All matter is composed of atoms, which have a nucleus composed of protons and neutrons around which electrons orbit. The number of atomic particles in the nucleus of an element’s atom determines its atomic weight, which is expressed in numbers that have bedeviled generations of high school chemistry students. When neutrons, protons, deuterons, and other particles strike a nucleus of high atomic weight, they are absorbed and the nucleus splits into two, forming two lighter atoms. The process releases a million volts of energy per atom. This process goes on continually in radioactive material but causes no trouble, because the released energy simply bypasses the other atoms in a block of material and passes into space.
However, by forming certain radioactive materials in a large enough and dense enough block, you have so many atoms in such limited space that a released neutron simply has to strike another nucleus, and particles released by that splitting of that atom will strike another nucleus. Then you have a chain reaction, with the energy in those trillions and trillions of atoms released all at once. Of the kinetic energy released in the chain reaction, about 50 percent forms a shock wave that flattens buildings, trees, and so on, the way a conventional explosion would. The main difference from conventional explosives is in the strength of the shock wave. The power of atomic bombs is measured in kilotons, each the equivalent of 1,000 tons of TNT, or megatons, the equivalent of a million tons of TNT. Thirty-five percent of the kinetic energy appears as heat, light, and ultraviolet radiation. The heat is radiated heat — infrared radiation — and travels at the speed of light. At the center of the explosion, the heat reaches 10,000,000 degrees centigrade. Conventional explosives may produce 5,000 degrees. The remaining 15 percent of the kinetic energy forms various nuclear radiations such as neutron rays and gamma rays, which are extremely destructive to living tissue. Some of this radiation kills or injures people in the initial spurt. More of it — about two thirds — is in radioactive dust that falls to earth. Some of this “fallout” may appear a few hours after the explosion, but fallout from a single explosion may continue falling for months or years, depending on how high it was blown into the atmosphere. It may be carried by the wind for thousands of miles.
Weapons using this “fission” reaction are commonly called “atomic bombs.”
There’s another process — fusion — that can produce even more powerful bombs.
This consists of combining the nuclei of two light elements. That forms an element that is lighter than the sum of the two elements that were combined.
The difference in mass is released as energy. The fusion of two light elements may release less energy than the fission of a heavy element such as uranium 235, but a chain reaction is different. Because light atoms are much smaller, there are far more of them in a given volume of material. A fusion bomb may release four times as much energy and six times more neutron rays than a fission bomb of the same size.
Fission bombs were the first kind developed. The most common fissionable materials are U-235 and U-233, unstable isotopes of uranium, and plutonium — a man-made element created by bombarding neptunium by deuterons or by performing other atomic hocus-pocus on uranium 238.
To reach a critical mass of plutonium 239, you need a lump of about 15 kilograms; for uranium 235, the critical mass is about 50 kilograms. There are two ways to make a critical mass in a bomb. One uses two pieces of the fissionable material, machined to extremely close tolerances to fit tightly together.
These are driven together in the bomb by explosive charges. When they meet, they form a critical mass and a nuclear explosion occurs. The second method uses a spongy ball of the fissionable material — full of holes so a fair proportion of the atoms are not in contact with other atoms. In this kind of bomb, explosives outside the fissionable material squeeze it together to form a critical mass.
Fusion bombs use light elements that fuse only when subjected to enormous heat. Hence they are called thermonuclear bombs. In these bombs, the heat is supplied by a fission explosion.
Much research on nuclear explosions has been directed at miniaturization.
The United States developed an enormous 280 mm howitzer, nicknamed the
