Did you know that Disney once inspired a bunker-busting bomb during the Second World War?
Read on to find out how and why.
What is a bunker buster and how do they work?
A bunker buster, like the modern "massive ordnance penetrator", is a specially designed type of munition that is specifically designed to penetrate hardened fortified structures that are often, but not always, buried deep underground. While modern examples tend to be precision-guided, early examples used other methods to penetrate structures, like submarine pens and bunkers, that would normally be considered impenetrable by conventional munitions.
Various examples were made during the Second World War with some of the most famous being the British "Tall Boy", "Grand Slam" and the "Disney Bomb," as well as various examples developed for the Luftwaffe and the American "Tarzon."
What was the "Disney Bomb"?
The "Disney Bomb" — sometimes referred to as the "Disney Swish" — was a rocket-assisted bunker-buster bomb developed during the Second World War by the British Royal Navy. The bomb, officially called the 4500 lb Concrete Piercing/Rocket-Assisted Bomb (~2000 kg), was specifically designed to penetrate hardened concrete structures, like submarine pens, that were designed to resist conventional free-fall bombing raids.
The bomb was designed by Royal Navy Captain Edward Terrel and was inspired, in part, by a World War II propaganda animated film by Disney entitled Victory Through Air Power. This novel piece of ordnance was fitted with solid-fuel rockets to help accelerate the speed of the bomb during descent.
The bomb was produced by Vicker Armstrong and used cordite as its propellant. Its payload consisted of Shellite high-explosive, and it was so big that it could only be deployed by large American bombers like the B-17 "Flying Fortress" and B-29 "Superfortress".
The bomb was 16 feet (5 mt) long, weighed 4,500 lbs (2,000 kg), had a diameter of 11 inches (280 mm) at its narrowest point, and 17 inches (430 mm) at its tail. This gave the bomb an impact speed of around 990 mph (1,590 km/h), which was significantly higher than the roughly 750 mph (1,210 km/h) free-fall terminal velocity of an equivalent 5-tonne "Tallboy" bomb.
The "Disney Bomb" would prove to be very effective, being able to penetrate around 16 feet (4.9 mt) of reinforced concrete before its explosive payload would detonate.
The bomb saw limited production and was only used in warfare by the United States Air Forces in the European theatre from February to April of 1945. While a technical success, initial applications of the bomb showed that the bomb was not particularly accurate, but devastating if it did hit the target.
As it was deployed fairly late in the war, its overall contribution to the defeat of the Axis forces was somewhat limited. It did, however, help inspire later iterations of "bunker-buster" bombs post-war.
Was the "Disney Bomb" inspired by a Disney film?
At the early stages of the Second World War, German U-boats were wreaking havoc amongst allied convoys. Working in so-called "Wolf Packs," they would prove very difficult to counter at sea.
Bombing raids on U-boat pens around the French and Norwegian coasts also proved ineffective as conventional bombs had little success in knocking them out.
By 1942, the British were getting desperate for a solution to the problem that was costing them dearly.
By pure coincidence, Disney had been asked by the U.S. government to produce a series of propaganda films to help inspire citizens after the attacks on Pearl Harbor and the declaration of war on the Axis forces.
One such film called "Victory Through Air Power" (released in 1943), including a scene that inspired the design of the "Disney Bomb." This animated film included a scene where rocket-powered bombs were used to penetrate and destroy German submarine pens.
It is said that after watching this film, British officers including Captain Edward Terrel were inspired to create a new kind of bomb that might turn the tide on the German U-boats.
Tentatively called the "Disney Bomb", its design built on previous work by Barnes Wallis, who had already developed two large "earthquake" bombs for the Royal Air Force. These included the 5-tonne "Tallboy" and 10-tonne "Grand Slam" bombs.
Being an expert of sorts when it came to the unconventionally-designed ordinance, Wallis developed the bombs to specifically be used against targets too heavily protected to remain unscathed by conventional high-explosive bombs.
These bombs were specifically designed to strike close to their intended target, penetrate deep into the earth, and cause major structural damage through the production of shock waves transmitted through the ground — hence the term "earthquake bombs".
During testing, these kinds of bombs proved more than capable of penetrating significant thicknesses of concrete (if a direct hit), despite not being designed specifically to do that.
In contrast, the "Disney Bomb" was designed from the start to penetrate concrete structures like the heavily reinforced roofs of bunkers. Whereas "Earthquake Bombs" were designed to target the entire structure, the "Disney Bomb" was designed to penetrate it and destroy the contents within.
For this reason, the "Disney Bomb" had an unusually thick steel shell that contained a relatively smaller amount of explosives. The "Disney Bomb" was also much more streamlined than other conventional heavy bombs.
These features were designed in accordance with Newton's approximation for the impact depth of projectiles and the empirical design equation known as Young's equation. This states that the deepest target penetration is achieved by a projectile that is dense, long, and thin (i.e. has a large sectional density), and strikes with a high velocity.
The British Admiralty was impressed with Terrel's idea, and production came under the British Ministry of Aircraft, which was in charge of making ordinance. After finally convincing both them and Churchill, the bomb went into production in 1944.
Were the "Disney Bombs" ever used?
The bombs were a British invention, but only certain American bombers were capable of carrying and deploying them. And this time during the war, only the American B-17 "Flying Fortress" was capable of performing such a task, and so the bombs were deployed under a joint defense technology-sharing agreement between the U.S. and the U.K.
The bombs were so large that they couldn't fit into the bomb bays, they needed to be carried under the wings. Bombers also had cameras fitted to track and monitor the trajectory of the bombs upon release.
Testing began in 1945, and using footage from the tests, engineers were able to make improvements to the design of the bomb to increase its accuracy and potency on impact.
The very first "Disney Bomb" attacks occurred in February and March of 1945, including on the Port of Ijmuiden in the Netherlands. This site had two fortified U-boat pens, one of which had a 14-foot (4.26 mt) reinforced concrete roof, the second 12-foot thick (3.65 mt) with a 3-foot (91 cm) air gap between another lower layer of concrete.
In February of 1945, 18 "Disney Bombs" were dropped on the two pens. The bombing proved successful enough to launch a second attack on the Valentin submarine pens in Rekum, Bremen in March of 1945. These pens were not complete and were in the process of developing type-21 U-boats prior to the assault.
Of the more than 60 "Disney Bombs" dropped, only one was precisely on target, but it proved devastating, as it managed to penetrate the 15-foot (4.57 mt) thick roofs of the pens and knock the facility out of action for the rest of the war.
Nearing the war's end, the last attack using "Disney Bombs" occurred on April 4th, 1945, in Hamburg. 24 B-17s attacked various fortifications around the city. A further mission in May 1945 was canceled.
By the end of the war, somewhere in the region of 158 bombs had been dropped on enemy forces and installations in four combat missions.
After the war, the British continued tests with the "Disney Bombs," still using American bombers. This ultimately led to the creation of "Project Ruby" — a joint project between the U.S. and U.K. to test and develop concrete penetrating bombs.
Captured German bunkers were used to test the capabilities of new bomb designs on the uninhabited island of Heligoland, as well as on the remaining Valentin submarine pens in Bremen.
These bombs were loaded with a variety of explosive charges. In all, 76 "Disney Bombs" were dropped during the Heligoland tests, each loaded with different explosive charges.
The average penetration was 14-feet 8-inches (4.46 mt) of concrete, with a maximum of 16 feet (4.87 mt).
The "Disney Bomb" was one of the most interesting pieces of ordinance developed during the Second World War. Inspired by a cartoon, it would do its part in helping break the German war machine.
While it was inspired by cartoonists, it would take the ingenuity and genius of British engineers to make it a reality.