The 12,000lb "Tallboy" (or "earthquake bomb") was the brainchild of British engineer Barnes Wallis, otherwise known as the "father of the bunker buster", who later devised the bouncing 22,000 lb spherical bombs used successfully against German dams in World War 2. Wallis also designed the required specially-modified Avro Lancaster bomber airframe to carry his impressive Tallboy bomb.
A Bomb That Could Explode Underground
Wallis believed in a large bomb capable of detonating underground near a buried target. He reasoned that such a weapon would transfer its explosive power (via shock waves) with more force than an above-ground explosion caused by a conventional dropped bomb. He devised this theory by watching bombs detonate, releasing their explosive energy and shock waves into the air. This new super bomb first had to be strong enough to penetrate deep within resistance material while also being able to produce the needed shock wave only after penetration. Bombs in World War 2 were constructed with a thin skin to reduce its overall weight during air transport by bombers and were relatively cheap to produce in quantity. Conversely, Each Tallboy bomb was cast with hardened high tensile steel that would allow the bomb to survive the impact from 20,000 feet of altitude or more. The purpose of such an earthquake bomb was to destroy a hardened target with benefit of increased shock wave energy transferred through material, earth or water against the target area itself, resulting in the protected target's damage or destruction. The structure would hopefully absorb the bomb's entire resulting energy instead of the energy being defused harmlessly in the air.
Not Like Other Drop Bombs
However, these new super bombs could not be mass-produced like conventional "dumb" drop bombs elsewhere. In fact, each were handmade to exact specifications and required relatively large amounts of production time and manual labor to complete. Additionally, the hardened steel skin was expensive to procure and accurate molding and tool & die work required clear-cut machining. For example, a precisely-tooled ogive (the roundly tapered end cap) was utilized, this essentially a large steel plug placed in the center "nose" of the bomb used to not only increase the bomb's ballistic weight during the drop but to also boost the bomb's penetrating power upon impact.
As such, the time and money needed to construct each bomb made them very valuable to warplanners. Their individual high cost of the Tallboy also dictated that they be used against high-value targets when standard bombing attacks would more than likely fail. Targets could include hardened underground bunkers, concrete tunnels within mountains and concrete dams powering towns and cities.
The Power Within
The primary explosive power of a Tallboy was Torpex. This material was 50% more powerful than TNT by mass and was composed of 40% TNT, 42% RDX (or cyclonite or hexogen) and 18% powered aluminum. All were melted together and poured by hand into the upside-down bomb casing. The last step was to pour one-inch of pure TNT followed by four inches of woodmeal wax over the top as a sealer surrounding three tubes that held the explosive booster and fuses.
Testing Forces Slight Changes
As evaluation bombs were dropped, the results shown the normal bomb shape was not aerodynamic enough to increase its own velocity during a drop and ensure penetration of the bomb to the required depth. After many shape variations were entertained, the solution was to increase the tail length of the bomb shape. The bomb alone was 10 ft (3m) long and the tail section was another 11 ft (3.3m) making the overall length of the Tallboy an impressive 21 ft (6m). Problems continued with the first prototypes tending to tumble during their fall so the tail was reconfigured once more and modified with a twist to generate a stabilizing clockwise spin as it fell. This new tail configuration also stopped any pitch or yaw effects and produced a gyro effect while maintaining the desired falling speed.
When dropped from 20,000 ft (6,100 m) the Tallboy recorded craters 80 feet deep (24 m) and 100 feet (30 m) across and could break through some 16 feet (5 m) of solid concrete. When the bomb exploded against the surface it would displace a million cubic feet (29,000 m≥) of earth and produced a crater that needed 5,000 tons of earth to fill it back to capacity. The Tallboy was a sound instrument and had a high terminal velocity with estimates during a fall ranging from 3,600 to 3,700 feet (1,100 m) per second (about 2,500 mph (4,000 km/h)). This velocity made the Tallboy faster than the speed of sound and, after the explosion, it was reported that one could still hear the noise of the bomb falling.
The bomb was fitted with three separate inertia pistols for triggered detonation. A preset time delay could be positioned to go off from 30 seconds up to 30 minutes to allow the bomb sufficient time to penetrate the ground target before exploding. Detonation was a major concern due to the bombs massive impact at 2,500 mph so three separate Type 47 long delay fuses were built inside the back of the bomb near the tail. This rear fuse device put the secondary detonation as far away from the bombs point of impact as possible improving the reliability of the fuse detonation. If two of the fuses do not successfully operate, odds were favorable that the third fuse would trigger the detonation of the Tallboy.
The Avro Lancaster is Drafted for Service
The readily-available, four-engined Avro Lancaster heavy bombers were tagged with supporting the Tallboy project. As such, the airframe had to undergo some modifications due to the excessive weight (12,000 lbs) and overall size of the Tallboys. Crews were also instructed on the flying altitudes recommended for the safe dropping of the bomb. These specially-modified aircraft also had their armor plating and defensive machineguns removed to reduce overall operating weight and the bomb bay doors had to be lengthened due to the bomb's 21 foot reach. However, the Lancaster was only inherently capable of reaching around a 25,000 ft (7,700 m) service ceiling, not the desired 40,000 ft bombing height that was recommended. As such, Lancaster crews had to make due and use care upon release. The aircraft bombardier was also trained to miss the target if the mission situation was not favorable and save the Tallboy for another day, this even though the Tallboy had the capability to punch through yards of concrete and meters of earth to destroy the target.
The Tallboy was first used in June of 1944 against the Saumur railroad tunnel. A Tallboy exploded as intended and blocked the tunnel some 60 feet deep into the mountain. Eight air raids using Tallboys were eventually flown against V-1 rocket and V-2 missile sites in France through "Operation Crossbow" between June and July of 1944, destroying many launch sites and slowing Hitlerís "vengeance weapon" programs. Dams were high-value targets as well and many were attacked in an effort to reduce local electric power to factories and bases. Additionally, they served well to flood French and German-held territories and cause logistical problems throughout. The Kemds Dam was hit by a Tallboy and destroyed while the Sorpe Dam was also hit and sustained a weakened structure.
Against the Tirpitz
Bombing sorties were also flown against the KMS Tirpitz German battleship on three occasions. In September of 1944, a Tallboy damaged the shipís bow, causing her to be modified into a gun platform. In October of 1944, another attack resulted in only minor damage to a propeller shaft. However, "Operation Catechism" during November of 1944 was enacted against the Tirpitz. This mission resulted in the dropping of three Tallboys, ultimately capsizing the German battleship and subsequently sinking her.
Against the U-Boats and the Lutzow
Tallboy bombs were also used against U Boat submarine pens across the French coastline from December of 1944 through April of 1945. Targeted sites included Ijmuiden, Bergen and Hamburg. The pocket battleship KMS Lutzow was also attacked in April of 1945 with fifteen aircraft and a near miss with a Tallboy sank her. However, this attack was conducted while the Lutzow was in shallow water so an effort to raise and repair her ensured that she would fight again.
To Berghof with Love
One of Hitler's vacation homes, Berghof, was attacked in April of 1945. Six Lancasterís of the 617 Squadron were called to drop their last Tallboys of the war and did so with some limited success.
It is reported that a total of 854 Tallboys were eventually dropped on the Reich during all of World War 2. Vickers was charged with production of the system.
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