On March 14, 1945, the British Air Force first used the Grand Slam seismic bomb. Let's remember what kind of ammunition it is.
The development of artillery, and then bomber aviation, forced the military to hide important objects not only behind thick walls, but also under a layer of earth. Underground structures have been a tough nut to crack for several decades, but the desire to destroy enemy targets and win over time has led to the emergence of new ideas. During the Second World War, British aircraft repeatedly used special ammunition designed to destroy railway tunnels, underground bunkers and factories.
Because of their principle of action, they are called "seismic bombs".
"Big" by engineer Wallace
At the very end of the thirties, an English aircraft designer and employee of Vickers-Armstrong Ltd. Barnes Wallace, confident in the need for massive strategic bombing of Germany, worked out options for promising aviation ammunition. Among other things, his attention was paid to underground concrete bunkers. According to Wallace's calculations, none of the then existing aerial bombs could destroy or at least cause significant damage to an underground structure with good protection. However, the designer was able to establish that in order to hit the target, the bomb must go deeper into the ground when it falls. In this case, the explosion would create a real seismic wave, which would ensure the destruction of the target. This principle is called the "seismic bomb".
Calculations of the same time made it possible to establish the optimal appearance of such an ammunition: a heavy streamlined bomb designed to be dropped from heights of at least 10-11 kilometers. In this case, the bomb could accelerate in the fall to a very high speed and, thanks to it, go deeper into the ground. The fuse was supposed to set up to detonate after penetration into the ground. The resulting small earthquake, depending on the power of the bomb, could destroy ground and underground structures within a radius of at least several tens of meters.
Unfortunately, the idea of a seismic bomb did not interest the British War Department and was shelved. A little later, in 1941, B. Wallace proposed a new concept for the original aviation ammunition - the so-called. jumping bomb to destroy dams. In May 1943, with the help of similar bombs, British aircraft destroyed two German dams and damaged another. Despite the relatively large losses during the sortie, the RAF recognized the effectiveness of Wallace's proposal. For this reason, the command asked him to continue research on the topic of seismic bunker bombs.
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By early 1944, Wallace had completed the design of the first seismic bomb, dubbed the Tallboy. The resulting ammunition fully justified its name: a teardrop-shaped body with a length of 6.35 meters and a diameter of 95 centimeters. The total weight of the bomb exceeded 5400 kilograms. It is worth noting that it was originally planned to make the original version of the bomb weighing ten tons, but the UK did not have an aircraft that could cope with such a load. Since the bomb was supposed to penetrate the ground and hit the target with minimal deviation, the designer applied several interesting solutions. Firstly, the body of the bomb had rather thick walls made of alloy steel. This feature of "Verzila" allowed in the future to enter the ground without noticeable deformations and damage. The second technical solution concerned the accuracy of the bombing. To prevent the ammunition from deviating from the calculated trajectory, it was equipped with four small stabilizers mounted at an angle. As a result, the bomb, gaining speed, spun around its axis and behaved like an artillery shell.
A seismic wave in the ground was created by a bomb charge: 5200 pounds (about 2360 kg) of torpex - a mixture of TNT, RDX and aluminum powder. This explosive has previously proven itself well in torpedoes. It was proposed to detonate the charge using a fuse, the type of which was suitable for a specific task. Fuse No. 47 with a moderator was considered the main one, but if necessary, contact fuse No. 58 could be used. The technology of making the bomb is interesting: molten torpex was poured into the molded body, installed vertically, after which it solidified. Due to the huge amount of explosives, this took several weeks.
To use the Tallboy bombs, the carrier plane had to be modified. The Avro Lancaster bombers, which were supposed to carry the bomb, have lost almost all armor plates and most of the weapons. Also, the aircraft's cargo bay underwent a significant alteration, which was equipped with new bomb bay doors and reinforced suspension devices. However, even in a lightweight version, the Lancaster could not lift Tallboy to an estimated height of 40 thousand feet (12.2 km). Therefore, in the course of test bombings, it was found out that it was enough for a bomber to fly at an altitude of 25 thousand feet (about 7.7 km) and this would be enough for the bomb to pick up the necessary speed in the fall. Finally, a special SABS scope was developed to provide the required accuracy.
During the tests, it was possible to find out the following feature of the ammunition. A Tallboy bomb falling from a design altitude could accelerate to a speed of about 1200 kilometers per hour, which exceeded the speed of sound. Such a supersonic bomb could penetrate up to 30 meters of dense soil or up to five meters of concrete. Further explosion was guaranteed to destroy the surrounding structures on the surface and - most importantly - underground.
Tallboy bombs were first used on the night of June 9, 1944 - on the very first night after the opening of the Second Front. The pilots of the 617th squadron of the RAF, by that time already bore the name "Dambreakers" (it was this unit that attacked German dams with "jumping bombs" a year ago) were tasked to destroy a railway tunnel near the city of Saumur. A total of 19 bombs completely destroyed the vaults of the tunnel. It is noteworthy that for the successful execution of the operation, only one hit was enough: one of the bombs hit exactly the tunnel, at a distance of about 60 meters from the entrance. "Tallboy" broke through the rock and the vault, and the explosion took place in the tunnel itself. As a result of this falling into the structure, about 10 thousand cubic meters of rock fell.
During the remaining months of the war in Europe, pilots from 617 Squadron dropped 854 Tallboy bombs. Various German fortifications and ships were attacked. The raids on the German battleship Tirpitz should be noted separately. During the first of these, on September 15, 1944, only one bomb hit the ship. The ammunition hit the Tirpitz's nose and made it impossible to move. On October 28, the bomb did not hit the ship, but its explosion nevertheless damaged the propeller shaft. Finally, on November 12, the pilots hit the ship three times. One of the bombs ricocheted off the armored tower and went into the water, while the other two pierced the deck and provoked a fire in the holds. As a result of the ignition of one of the powder magazines, an explosion tore off the gun turret. Soon the battleship sank. During the last raid on "Tirpitz" the British lost only one plane, which made a hard landing in neutral Sweden.
"Big cotton"
At the end of June 1944, the RAF attempted a raid on a German underground plant in the Wieserne Dome bunker (also known as the Elfo Dome). The dropped Tallboy bombs were able to damage some parts of the structure of the bunker dome, but none of them coped with the dome itself. In connection with this incident, work on the ten-ton seismic bomb was resumed at Vickers under Wallace's leadership.
Structurally, the new ammunition called Grand Slam ("Big Cotton") was an enlarged version of the "Verzila". The body of the bomb was lengthened to 7.7 meters, and the diameter increased to 1.17 meters. The mass increased accordingly - to almost ten tons, of which 9140 pounds (about 4500 kg) were torpex. This amount of explosive after pouring cooled down for almost a month. During testing, the Grand Slam bomb showed approximately the same speed indicators as the previous Tallboy. She also accelerated to supersonic speeds, but showed the best penetration rates. "Grand Slam" buried 35-40 meters into the ground and at the same time it was much better than "Tallboy" to break through concrete barriers. Part of the test bombings using Grand Slam ammunition were carried out on the captured Wieserne Dome bunker. The dome of the building was severely damaged, but still resisted. Nevertheless, the characteristics of the new bomb were considered sufficient for practical use.
The “Big Cotton” was first played on March 14, 1945, near the town of Bielefeld. During the raid on the railway viaduct, the pilots of the 617th squadron dropped one new bomb and several Tallboy ammunition. The explosions destroyed about 30-35 meters of the structure. The next day, the viaduct at Arnsberg was similarly hit. However, this time two Grand Slam and 14 Tallboy bombs did not produce tangible results: the structure of the viaduct was damaged, but this damage was insufficient to destroy it.
Active operations of the British aviation with the use of seismic bombs of both types continued until mid-April. During this time, the pilots of the 617th Squadron dropped 42 Big Cotton bombs and destroyed a large number of targets. The raid on the Valentin bunker was considered particularly successful. In this structure, it was planned to make a new plant for the construction of submarines. The roof of the bunker in some places was up to seven meters thick. During the raid on March 27, 1945, two Grand Slam bombs got stuck in the roof of the structure in an area about 4.5 meters thick and exploded inside the concrete structure. Part of the roof collapsed, and the remaining ceilings cracked and could not be repaired.
American record
Seeing the effectiveness of British bunker bombs, the United States also began a similar project. However, taking into account the experience of using Tallboy and Grand Slam, the Americans changed the appearance of a promising bomb. First of all, the mass and, as a result, the dimensions of the ammunition were subjected to adjustments. Calculations showed that a bomb with a total weight of about 18-19 tons was required to ensure the destruction of the then existing and promising bunkers. The project was indexed T-12 and codenamed Cloudmaker.
The American bomb was an enlarged version of the British ammunition. During the development, however, it was necessary to take into account some technological nuances, due to which the weight of the finished bomb went beyond the intended framework. The finished Cloudmaker weighed 20 tons and was about twice the size of the Tallboy. Torpex explosive charge is about eight tons. The weight and dimensions of the new seismic bomb were such that it could only be carried by one aircraft - the Convair B-36 Peacemaker bomber.
However, the Peacemaker did not immediately carry the T-12 bomb. First, they made several test drops from a smaller aircraft, the Boeing B-29 Superfortress. A serial bomber was specially altered for testing. It was made as easy as possible by removing all unnecessary parts (armor and weapons), the cargo compartment was altered to accommodate large ammunition, and the amount of fuel to be poured was calculated accordingly. Until the first test bomb was dropped, everyone involved in the project was very nervous: he could not say how the bomber would behave, the maximum take-off mass of which was only three times the mass of the bomb. The designers feared that the aircraft freed from the load would throw up, and the resulting overload would damage its structure. Fortunately,the test pilots coped with the sudden pitching up and the B-29 returned safely to its airfield.
According to some reports, during the tests, a T-12 bomb dropped from a height of ten kilometers pierced up to 50-55 meters of soil or up to 8-10 meters of concrete. Thus, the capabilities of the new American ammunition were significantly higher than that of any other bomb of this class.
In addition, due to the principle of its action, a buried seismic bomb in some cases could be more effective than nuclear weapons exploding in the air or on the surface of the earth.
Soon after the start of testing on the B-29, the first Cloudmaker dropped from the B-36 aircraft. For a heavy strategic bomber, this procedure was perfectly safe, although the Peacemaker had to be redone accordingly. In January 1949, as an experiment, one B-36 took off at once with two T-12 bombs. The flight proceeded without incident, although the bomb load of 43 tons (two bombs and suspension devices for them) exceeded the maximum permitted.
In the same 1949, the T-12 Cloudmaker bomb was adopted. Around the same time, the chiefs of the Pentagon finally decided on the priorities for the development of their air forces. Now the B-36 strategic bombers were viewed exclusively as carriers of nuclear weapons. Cloudmaker bombs, which have a specific tactical niche, have lost their priority. Finally, in the mid-fifties, American nuclear engineers created several new nuclear bombs that acted like the existing seismic bombs: they "stuck" into the ground and exploded there. This ammunition turned out to be much smaller and lighter than the Cloudmaker, which is why they could be transported not only by the B-36, but also by other American bombers of the time.
The T-12 Cloudmaker seismic bomb remained in service with the US Air Force until the late fifties. On February 12, 1959, the command ordered the decommissioning of the B-36 bombers. Since no other aircraft could use the T-12 super-heavy bomb, it was also removed from the US Air Force's weapons list. In the future, the United States did not deal with the subject of super-large-caliber bunker bombs. This niche was firmly occupied by less heavy ammunition with sufficient characteristics. In addition, over the past decades, the acceleration of a bomb to the required speed has been carried out not in free fall, but with the help of a solid-propellant accelerator. The time of huge seismic bombs weighing several tons has passed.
However, when the US Army needed a non-nuclear weapon to destroy heavily fortified targets during Operation Desert Storm, the idea of a seismic bomb was revived by a group of engineers from the Armament Systems Division. In the shortest possible time, they created a GBU-28 guided bomb weighing 2300 kg. The bomb is capable of penetrating more than 30 m of soil or 6 m of concrete. This weapon was successfully used against an underground military complex near Baghdad.
