page_title: Bunker buster
section_title: United Kingdom
hierarchical_section_title: Bunker buster / Aircraft delivered bombs / World War II / United Kingdom
caption_attribution_description: English: The impact crater in the roof of the Valentin submarine pens, produced by a British, World War 2, Disney rocket-bomb during post-war testing.
context_page_description: A bunker buster is a type of munition that is designed to penetrate hardened targets or targets buried deep underground, such as military bunkers.
context_section_description: In World War II, the British designer Barnes Wallis, already famous for inventing the bouncing bomb, designed two bombs that would become the conceptual predecessors of modern bunker busters: the five tonne Tallboy and the ten tonne Grand Slam. These were "Earthquake" bombs—a concept he had first proposed in 1939. The designs were very aerodynamic, allowing them to exceed the speed of sound as they fell from 22,000 ft (6,700 m). The tails were designed with offset fins causing the bombs to spin as they fell. Using the same principle as a spinning top, this enabled them to resist being deflected, thereby improving accuracy. They had casings of high grade steel, much stronger than the typical World War II bomb so that they would survive hitting a hardened surface, or penetrate deep into the ground.
  Though these bombs might be thought of as 'bunker busters' today, in fact the original 'earthquake' theory was more complex and subtle than simply penetrating a hardened surface. The Earthquake bombs were designed not to strike a target directly, but to impact beside it, penetrate under it, and create a 'camouflet' or large buried cavern at the same time as delivering a shock wave through the target's foundations. The target then collapses into the hole, no matter how hardened it may be. The bombs had strong casings because they needed to travel through rock rather than reinforced concrete, though they could perform equally well against hardened surfaces. In an attack on the Valentin U-Boat pens at Farge, two Grand Slams went through the 15 ft (4.5 m) reinforced concrete hardening—equalling or exceeding the best current penetration specifications.
  The British Disney bomb (officially "4500 lb Concrete Piercing/Rocket Assisted bomb") was a World War II device designed to be used against U-boat pens and other super-hardened targets. Devised by Captain Edward Terrell RNVR of the Admiralty's Directorate of Miscellaneous Weapons Development, it had a streamlined hardened case and weighed some 4,500 lb (2,000 kg) including the rocket assembly. The actual explosive content was about 500 lb (230 kg).
  For accuracy, the bombs had to be dropped precisely from a pre-determined height (usually 20,000 ft (6,100 m)). They would free-fall for around 30 seconds until, at 5,000 ft (1,500 m), the rockets were ignited, causing the tail section to be expelled. The rocket burn lasted for three seconds and added 300 ft/s (91 m/s) to the bomb's speed, giving a final impact speed of 1,450 ft/s (440 m/s; 990 mph), approximately Mach 1.29. Post-war tests demonstrated that the bombs were able to penetrate a 14-foot-8-inch (4.47 m) thick concrete roof, with the predicted (but untested) ability to penetrate 16 feet 8 inches (5.08 m) of concrete.
caption: Diagram of a roof penetration produced by a Disney bomb striking the German, Valentin U-boat pen. The bomb was one of a number dropped on the bunker during post-war testing[2]
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