Wallis foresaw a series of 6,000lb, 12,000lb, and 22,000lb weapons, with the codenames Tallboy Small, Medium, and Large being assigned. It was thought that a drop altitude in excess of 40,000 feet might be necessary, so Wallis went so far as to sketch out a new high performance aircraft, the Victory bomber, to carry the Tallboy. This was not proceeded with, although the Vickers Windsor stemmed in part from the Victory concept.
The 6,000lb bomb never materialized, but the 12,000lb weapon (known thereafter simply as Tallboy) was ready for action by the summer of 1944. Some 21 feet in length and 38 inches in diameter at the widest point, Tallboy contained over 5,000lbs of Torpex, a high explosive considerably more energetic than TNT. Striking its target at supersonic speed, Tallboy could produce a crater 100 feet wide and almost as deep. Alternatively, the weapon could break through up to 16 feet of concrete.
617 Squadron, although having lost its capability to deliver the Upkeep bomb, remained a "special" unit, and was chosen to carry out operations with the new Wallis weapons. In order to accommodate the massive Tallboy, the Lancaster needed to have special bulged bomb bay doors fitted. The unit conducted the first combat drop of Tallboy on June 8, 1944 when the railway tunnel at Saumar in the Loire Valley was attacked. Of the eight aircraft used, five were lost, but the tunnel was indeed closed, restricting the Germans' ability to respond to the Allied invasion of Normandy.
Tallboy's most famous usage was against the German battleship Tirpitz. The Bismarck's sistership had only taken to sea a few times since being completed in 1941, but her very existence tied down a considerable number of Allied ships. Kept in Norwegian fjords, Tirpitz was a major threat to convoys on the run to Murmansk, while presenting an almost impossible target to destroy. Short of luring Tirpitz out to sea for decisive naval battle, carrier raids and unconventional actions seemed to be the only hope of dealing with her.
Tallboy was used against Tirpitz three times. The first raid took place on September 15, 1944 when 27 Lancasters bombed the battleship at the fjord at Kaa. This was too far away to be reached from any UK base, so the Lancs had been forward deployed to a Russian airfield near Archangel. When the bombers arrived over the fjord, they encountered heavy resistance, and it was thought that no hits had been achieved.
Despite the seeming failure of the September mission, the RAF was by no means done with Tirpitz. The Lancaster crews had actually done better than they thought, as the raid had indeed resulted in one strike on the ship. One bomb had passed all the way through the forecastle and out through the bottom of the hull, before exploding. This was not enough to sink Tirpitz, but the resulting damage did severely limit her top speed to no more than 10 knots. This essentially ended her career as a fleet unit, as she would have been easily sunk during any attempt to bring her back to Germany for major repairs.
Anticipating that the Allies might undertake amphibious landings in Norway, the Germans moved Tirpitz south to Tromso, where a trench was dredged in shallow water. Placed there, Tirpitz could act as a stationary artillery hulk. However, the move also meant that the ship could be reached, albeit just barely, by Lancasters operating from Lossiemouth in Scotland. Once the British had found Tirpitz again, preparations began for just such a mission. These included fitting 617 Squadron aircraft, along with some borrowed 9 Squadron examples, with additional fuel tanks and Merlin 24 engines to cope with the increased weight.
On October 29, 1944 the Lancasters set out for Tromso from Scotland, but the fjord's defenses knocked down several aircraft, and only one near miss was achieved. Undaunted, Bomber Command staged yet another raid on November 9. This time, the defending fighters, artillery, and smoke screen generators were caught by surprise. At least two and probably three Tallboys hit Tirpitz, with several others landing nearby. This finally dealt a conclusive blow to the last German battleship, with a magazine explosion and massive flooding quickly sealing Tirpitz's fate. Quickly capsizing, the ship took up to 1,000 men to their deaths.
Tallboy was also used against another major German surface combatant, the heavy cruiser Lutzow, the "pocket battleship" formerly named Deutschland. One of the last major Kriegsmarine units to remain afloat as the Third Reich crumbled, Lutzow was located in the Baltic harbor of Swinemunde. Although having been inactive for some time, Lutzow was still capable of action, and in any case there was probably the desire to deny the ship to the approaching Soviets. A pair of raids were launched against the ship by 617, but bad weather prevented any bomb drops. Finally, on April 16 the clouds cleared and Lutzow's fate was sealed. A hail of Tallboys and 1,000lb bombs descended, and at least three hit the ship or came close. These holed her sufficiently to sink her in the shallow harbor, and although the Germans were able to use her as a static battery, she never again moved under her own power.
By late April 1945 the strategic bombing campaign against Germany was over, but there were still important targets to be hit as Allied armies closed in on the last German bastions; one of these was Hitler's Eagle's Nest headquarters at Berchtesgarden This was to be the target of a massed raid by nearly 350 Lancasters on April 25, with Mosquitoes also taking part. Most of the Lancs were armed conventionally, but 16 examples were from 617 Squadron, which dropped the last Tallboys to be used in anger by the RAF.
TARZON
(USAF)
This was not the end of the Tallboy story, however, as the design also served as the basis for the American VB-13 / ASM-A-1 Tarzon heavy guided bomb, carried by B-29s. This used the basic Tallboy body mated to a radio control system, box tail, and a circular wing mounted around the weapon's midbody. The end of the war put the Tarzon program on hiatus, but the effort was revived when the US went to war in Korea. A number of Tarzons returned from storage were used against North Korean bridges starting in December 1950, but there were a number of difficulties that kept the system from being used to its full potential - the bombs were old, their explosives deteriorating, and the system had not been thoroughly proved out in the first place. Tarzon operations ended in August 1951 after the loss of one of the B-29 launch aircraft.
GRAND SLAM
The last of Wallis' penetrating bombs was the Grand Slam 22,000lb weapon, originally known as the Tallboy (Large). At 26.5 feet in length and 46 inches in diameter, Grand Slam's dimensions were not dramatically larger than those of Tallboy, but the later bomb had an explosive charge almost twice that of its predecessor.
The job of carrying Grand Slam was allocated to the Lancaster B 1 (Special), just over thirty of which had been supplied to 617 Squadron. The refit process for the airframe was fairly extensive, given the bomb's dimensions and the fact that it weighed nearly as much as the Lancaster itself. The only defensive armament retained was the tail turret, and the bomb bay doors had to be removed. Since a loaded B1 (Special) was considerably heavier than a standard Lancaster, use of the stronger the landing gear designed for the Avro Lincoln was necessary.
Grand Slam was not available until the very last stages of the war in Europe, but even then suitable targets were still to be had. The Bielefeld Viaduct was one example; this massive structure carried rail lines over the River Werre, and had proven to be virtually untouchable by conventional bombing; even a raid on February 22, 1945 using Tallboys had not been able to knock it out. Finally, on March 14, 617 dealt Bielefeld a crippling blow during the course of the first Grand Slam mission. Most of the Lancasters involved were again armed with Tallboys, but two had Grand Slams. One aborted before making to the target, but the other successfully dropped its weapon, which helped destroy hundreds of feet of the viaduct. By the end of the war, 41 Grand Slams had been dropped on targets like the massively reinforced U-Boat pens near Bremen.
The US adopted the Grand Slam as the T-14 / Mk. 110, and conducted trials of the weapon from B-29s. The Superfortress could carry a single Grand Slam in the bomb bay although the lack of ground clearance mandated the use of a loading pit. A pair of T-14s could be carried externally on underwing pylons. But even the Grand Slam would be dwarfed by the US T12 Cloudmaker, a massive 43,000lb weapon derived from Wallis' work and intended for use from the B-36 Peacemaker. A test B-29 dropped the first Cloudmaker in March 1948, and in January of the following year a B-36 had demonstrated its enormous lifting potential by dropping a pair of T12s.
