October 26, 2011: The last of the large American nuclear weapons, a four ton B53 atomic bomb is being dismantled. With a yield of 9 megatons (of equivalent conventional explosives), the B53 was one of the most powerful nuclear weapons the U.S. ever placed into service. A version of the B53 was used on the Titan II ICBM. The B53 entered service in 1962, and the last fifty (of 340 built) were retired in 1997. It's taken so long to dismantle all of them because it was a large, and complex, weapon. This was compounded by poor documentation, and the fact that the original designers were now dead or too old to remember crucial details needed by those disassembling the weapons.

The B53 was designed in the 1950s and replaced 500  B41s, which had a yield of 25 megatons. The largest nuclear device ever built and tested was the 27 ton Russian AN602, which had a yield of 50 megatons. It was eight meters (26 feet) long and 2.1 meters (6.9 feet) in diameter. Only one of these was built. The Russians followed the Americans in phasing out large yield bombs in favor of smaller, and more numerous ones. This was largely the result of ICBM warheads designed to carry multiple nuclear weapons.

The B53 was 3.8 meters (12.5 feet) long and 1.27 meters (50 inches) in diameter. In effect, the size of a small truck. Air force personnel called the B53 the "last of the big dogs." After the B53, nukes got a lot smaller. Some of those are still in service.

One of the best examples of the next generation of U.S. nuclear bombs was the American B61. About the same shape as a 1,000 pound (455 kg) bomb, many NATO fighter bombers were equipped (with the electronics) to use this bomb during the Cold War (and many can still do so). Some 3,200 B61s were built since it entered service in the late 1960s, and about a third of those remain available for use. Some are to be refurbished, but politicians are still debating doing this just to keep B61s good for another two decades. Without the refurb, all these older warheads will be useless in less than a decade.

In 1997, a bunker buster version of the B61 entered service. This was your basic B61 with a metal penetrator cap at the front end. This kind of B-61 would penetrate several meters of earth before setting off its nuclear warhead (probably 10 kilotons, but could be as high as 340). The basic B61 nuclear bomb weighs 319 kg (700 pound), is 330mm in diameter and 3.9 meters (12.6 feet) long. Most B61 warheads were variable yield, and could be set to provide an explosion ranging from less than a kiloton, to 340 kilotons.

For a long time, many of the "tactical" nukes, like the B61, were deployed close to where the fighting was expected to be. Thus during the early 1970s, the United States had over 7,000 nuclear warheads stored in Europe, most of them 8 inch and 155mm artillery shells. This was in the belief that, if the Russians, and their Warsaw Pact allies, invaded Western Europe, they would do so using these "tactical" (a yield of under 100 kilotons) nuclear weapons. Plans were drawn up to use hundreds of these warheads in battles with the invading Russians. But eventually, it was realized that such use would destroy Western Europe, and probably lead to a full scale nuclear war that would devastate the planet. So, by the end of the Cold War in 1990, there were only about 4,000 U.S. nukes left in Europe. By the end of the 1990s, there were only about 500 left. That number has since declined to less than 200. Most of these were for the use of NATO allies. During the Cold War, European nations were to be provided with American nuclear weapons, in the event of a major war. Most of these agreements are still in effect.

The U.S. Air Force still trains it pilots to use the B61, using dummy 1,000 pound bombs, filled with enough concrete to approximate the weight of a B61. In the case of the bunker buster B61, that would be 546 kg (1,200 pounds). The Department of Defense wants to equip the F-35 to use B61s.