How Nuclear Bombs Work

Nuclear Bomb Delivery

An atomic bomb of the 'Little Boy' type that was detonated over Hiroshima Japan
An atomic bomb of the 'Little Boy' type that was detonated over Hiroshima Japan

It's one thing to build a nuclear bomb. It's another thing entirely to deliver the weapon to its intended target and detonate it successfully. This was especially true of the first bombs built by scientists at the end of World War II. Writing in a 1995 issue of Scientific American, Philip Morrison, a member of the Manhattan Project, said this about the early weapons: "All three bombs of 1945 -- the [Trinity] test bomb and the two bombs dropped on Japan -- were more nearly improvised pieces of complex laboratory equipment than they were reliable weaponry."

The delivery of those bombs to their final destination was improvised almost as much as their design and construction. The USS Indianapolis transported the parts and enriched uranium fuel of the Little Boy bomb to the Pacific island of Tinian on July 28, 1945. The components of the Fat Man bomb, carried by three modified B-29s, arrived on August 2. A team of 60 scientists flew from Los Alamos, N.M., to Tinian to assist in the assembly. The Little Boy bomb -- weighing 9,700 pounds (4,400 kilograms) and measuring 10 feet (3 meters) from nose to tail -- was ready first. On August 6, a crew loaded the bomb into the Enola Gay, a B-29 piloted by Col. Paul Tibbets. The plane made the 750-mile (1,200-kilometer) trip to Japan and dropped the bomb into the air above Hiroshima, where it detonated at exactly 8:12 a.m. On August 9, the nearly 11,000-pound (5,000-kilogram) Fat Man bomb made the same journey aboard the Bockscar, a second B-29 piloted by Maj. Charles Sweeney. Its deadly payload exploded over Nagasaki just before noon.

Today, the method used in Japan -- gravity bombs carried by aircraft -- remains a viable way to deliver nuclear weapons. But over the years, as warheads have decreased in size, other options have become available. Many countries have stockpiled a number of ballistic and cruise missiles armed with nuclear devices. Most ballistic missiles are launched from land-based silos or submarines. They exit the Earth's atmosphere, travel thousands of miles to their targets and re-enter the atmosphere to deploy their weapons. Cruise missiles have shorter ranges and smaller warheads than ballistic missiles, but they are harder to detect and intercept. They can be launched from the air, from mobile launchers on the ground and from naval ships.

Tactical nuclear weapons, or TNWs, also became popular during the Cold War. Designed to target smaller areas, TNWs include short-range missiles, artillery shells, land mines and depth charges. Portable TNWs, such as the Davy Crockett rifle, make it possible for small one- or two-man teams to deliver a nuclear strike.