The Evolution of the Nuclear Bomber

At the end of World War II in August 1945, the United States had a total of 15 B-29 strategic bombers capable of delivering nuclear weapons. Today, the US maintains a ready strategic fleet of 76 B-52s, 63 B-1s, and 20 B-2 stealth bombers. In all, some 4800 strategic nuclear bombers were built between 1945 and 2014.

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B-29 bomber “Enola Gay”, on display at the Smithsonian’s Udvar-Hazy Center.

By mid-1943, the Manhattan Project, the super-secret military program that was developing the atomic bomb, had a pretty good idea what the gun-type uranium bomb design known as Thin Man and the implosion-type plutonium bomb known as Fat Man would look like–the Fat Man would be roughly ten feet long and weigh about five tons, while the Thin Man would be somewhere around 20 feet long. The standard British bomber at that time, the Avro Lancaster with its 33-foot long bomb bay, was capable of carrying this, with some modifications, but the US military wanted to use one of its own planes.

The standard American bomber, the B-17, was not capable of carrying such a load, but the new B-29 Superfortress, just entering production, could handle it if some alterations were made. So almost as soon as the first B-29s went into service in July 1943, technicians from the Manhattan Project obtained a number of the bombers, assigned them to the 509th Composite Bombing Group, and began testing a variety of modifications. At first, the normal two B-29 bomb bays were cut to produce one single large bomb bay, capable of holding the proposed Thin Man design. But in mid-1944 the Thin Man design was dropped in favor of the much smaller Little Boy, which could fit into a standard B-29 bomb bay. As a result, the standard B-29 bomb bays were now left intact, and the release mechanism in the forward bay was heavily modified to hold a single very heavy bomb. The B-29’s weight was reduced by removing all the armor plating and gun turrets, and in 1945 early versions of the new fuel-injected engine were added for more power. The modified B-29s were given the codename “Silverplate”. A total of 46 Silverplate B-29s were made during the war, with 15 assigned to operational combat duty (the rest were for testing and training).

Almost immediately after the Second World War ended, the Cold War began, which became especially heated after the Soviet Union developed its own atomic bomb in 1947. Now, the United States faced the prospect of a nuclear war with a target that was half the world away. The Pentagon had ordered a further 19 Silverplate nuclear-capable B-29s to be delivered in 1946 and 1947, but now they wanted a bomber that would be capable of reaching the USSR from airfields in the United States, and the B-29 could not do that.

A solution was already in the works. In 1940, before the US even entered the war, President Franklin D Roosevelt knew that he would eventually have to fight the Nazis, and in the dark days of the fall of France and the Battle of Britain, it looked as if the Germans might succeed in conquering all of Europe. That would mean the United States would have no choice but to bomb Nazi targets in Europe using bombers that were based in the United States, a roundtrip flight of 6,000 miles. The project was put on the back burner for a time, in favor of the also already-planned B-29, but in 1942 it took on a renewed urgency as the US lost all its bases in the Pacific, and was faced with the possible necessity of bombing Japan from bases in Hawaii. The Pentagon quickly drew up plans for a massive six-engined bomber that could deliver five tons of bombs at 40,000 feet to targets 4,000 miles away. Known as the B-36 “Peacemaker”, it would be built by the Consolidated (Convair) Company. The Army Air Force ordered 100 of them before the prototype was even built.

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B-36 Peacemaker, parked next to a B-29.                    US Air Force photo

As the Pacific War turned in the US’s favor and B-29s began firebombing Japan from bases on Saipan and Tinian, the B-36 fell in priority, but delivery of the first planes was still scheduled for August 1945, in time for the planned invasion of Japan in October. In the end, delivery was delayed by production issues, and the first B-36s were not delivered until August 1946, long after the Silverplate B-29s had ended the war.

The new B-36, at a wingspan of 232 feet and a weight of 72,000 pounds, dwarfed the B-29. Its six huge propeller engines, mounted at the rear edge of the wings, made it the only American plane in service that could reach the Soviet Union from the United States, and also the only one with a bomb bay big enough to carry the huge Mark 16 and Mark 17 hydrogen bombs. The crew of 15 would be airborne for up to 40 hours at a stretch: the plane was therefore fitted with bunk beds and a dining room.

But as a piston-engined propeller-driven bomber, the B-36 was obsolete from the day it was deployed. The fuel tanks were located in the wings, and they often developed leaks from the vibrations. Meanwhile, the backwards-mounted engines often developed oil leaks and were prone to catching fire. The takeoff distance for the big lumbering beast was too much for many American runways, so it was fitted with four JATO (Jet-Assisted Take-Off) engines on the wings to help it take off.

Nevertheless, the B-36 Peacemaker became the backbone of the US Air Force’s Strategic Air Command from 1947 to 1955. Under General Curtis LeMay, SAC kept a proportion of its B-36s on constant standby, ready to bomb the USSR at a moment’s notice. They also spent a lot of time on long cross-continent flights over the US or across the Atlantic Ocean to Europe, making practice bombing runs on unsuspecting cities (while carrying actual unarmed nuclear weapons).

But even as the B-36 was being deployed in 1947, the US already had a jet-powered nuclear bomber in the works, known as the B-47 Stratojet. Built by Boeing, the B-47 had a crew of just three, and was the first US bomber to have swept wings and also the first to use solid-state electronics components. The B-47, however, had what, to American war planners, were two crippling flaws: it did not have the range to reach the Soviet Union from American bases without aerial refueling (which was then still in its infancy), and it could not carry the largest of the American thermonuclear bombs. There were other problems. Even with its six jet engines, the B-47 required such a long distance to take off that it was almost immediately modified by adding RATO (Rocket-Assisted Take-Off) pods, essentially small rockets under the wingtips that would help accelerate it down the runway. Conversely, it took such a long distance to stop at landing that it was fitted with a parachute in the tail to help slow it down. While cruising at high altitude, its performance envelope was only 8 mph wide–just 4 mph too slow and it would stall, just 4 mph too fast and vibrations would shake the wings apart.

The B-47 flew with SAC from 1951 to 1965.

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B-47 Stratojet                      US Air Force photo

From the moment the B-47 was delivered, Boeing recognized its problems and learned from the experience. Boeing’s next design, a swept-wing eight-engined jet bomber known as the B-52 Stratofortress, incorporated all the lessons it had learned from the B-47. The B-52 can travel at 650 mph and reach altitudes of 50,000 feet, and can travel an incredible 10,000 miles without refueling, enough to go from California to Moscow and back. Using aerial refueling from tanker planes, the B-52 can fly nonstop completely around the world in 46 hours. Different versions had a crew of between 6 and 9 people. First deployed in 1955, the last B-52s stopped rolling off the assembly line in 1962, and this last batch of 85 aircraft is still in service today. Over the decades the B-52 has undergone numerous modifications, allowing it to carry everything from gravity bombs to cruise missiles and armed drones.

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B-52 Stratofortress                             US Air Force photo

The planned replacement for the B-52 was the Convair B-58 Hustler. With its delta wing and streamlined engine pods, the B-58 looked more like a fighter than a bomber. It was specifically designed to defeat Soviet air defenses by going in to its target high and fast. Its four jet engines could push it to Mach 2, twice the speed of sound. Even the material it was made from was futuristic–the aircraft’s skin was called “mag-thor”, an alloy of magnesium and thorium which was actually radioactive, though not enough to present a danger to the crew of three. The B-58 was however a very difficult plane to fly: of the 116 built (30 were used only for testing and training), 26 were destroyed in crashes. The aircraft was also crippled by its limited fuel capacity and range. Finally, the development of Soviet radar-guided surface-to-air missiles made all high-altitude bombers vulnerable, no matter how fast they were. The Hustler was converted from a bomber into a fast reconnaissance plane, and was then withdrawn from service by 1970.

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B-58 Hustler                                  US Air Force photo

During this time, the B-1 Lancer nuclear strategic bomber was already on the drawing table. Originally designed in the 1960’s as a high-altitude supersonic replacement for the B-52, it was changed in the 1970’s to a low-altitude high-speed bomber that could slip underneath Soviet radar and avoid surface-to-air missiles. The whole project was cancelled by President Carter, then restarted by President Reagan and finally deployed in 1986. Almost immediately, it was rendered obsolete by the development of “stealth” technology, but the Pentagon decided to go ahead with the bomber anyway as a stopgap between the planned retirement of the B-52 and the deployment of the new stealth bomber. When the Cold War ended in 1991, the B-1 lost its primary reason for existing, and although it was used for some conventional bombing in Iraq and Afghanistan, it has been largely rendered useless.

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B-1B Lancer                         US Air Force photo

The Boeing B-2 Spirit was the last of the Cold War nuclear bombers. By taking advantage of new stealth technology, which consisted of radar-absorbent coatings, careful geometry to avoid radar reflections, and technical methods of reducing the heat signature from engines and aerodynamic surfaces, the B-2 was designed to penetrate Soviet air defenses by remaining virtually invisible to radar. It was deployed in 1989, just as the Cold War was coming to an end. Reassigned to the conventional bombing role, the B-2 saw its combat debut during the 1991 Iraq War, when it took off from American bases in the Indian Ocean to strike air-defense targets in Baghdad.

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B-2 Spirit                       US Air Force photo

Today, the strategic nuclear bomber is all but obsolete. Even before the end of the Cold War, its role had already been taken over by the nuclear-armed cruise missile. In the 21st century, armed Unmanned Air Vehicles (UAVs) are performing the majority of conventional bombing missions.

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4 thoughts on “The Evolution of the Nuclear Bomber”

  1. Kind of ironic that an engineer from Nazi Germany was instrumental in making the nuclear bomber obsolete… 🙂

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