Tallboy (bomb)

Tallboy bomb

The Tallboy was an earthquake bomb developed by Barnes Wallis and brought into operation by the British in 1944. It weighed five tons and, carried by the Avro Lancaster bomber, was effective against concrete structures against which earlier, smaller bombs had proved ineffective. It came about as a compromise from Wallis' original plan for a 10 ton bomb dropped from 40,000 ft (the Earth Quake Bomb concept) which was not at the time possible. Later on in the war, a 10 ton bomb was created and used successfully.

History

The size of aerial bombs available up to this time, and the difficulties in accurately hitting targets meant that bombing raids against any massive or protected structures had been pointless.

The British engineer Barnes Wallis had earlier considered the strategic use of bombs as a means to destroy the enemy's capacity to wage war by hitting its infrastructure and manufacturing bases and to this end developed improved bomb designs based on large single bombs early in the war. He had presented his ideas for a 10 ton bomb working on the earthquake principle in his famous paper A Note on a Method of Attacking the Axis Powers in 1941.

His calculations showed that a very large bomb exploded deep underground beside a target would form a camouflet (cavern) rather than a crater. All the explosive energy would be contained within the ground and the shock transmitted into the foundations of the target, which would then collapse into the camouflet. More importantly, the shockwaves transmitted though a non-compressible medium are less attenuated by distance than a compressible medium such as air. The bouncing bombs that destroyed dams used this principle by using water as the non-compressible medium. If such a large bomb were exploded closer to the surface a huge single crater would be created, which would tax the capability of earthmoving equipment to fill in, and could effectively disrupt targets such as railway marshalling yards for long periods.

However, the carrying capacity of British bombers was limited and the capability to carry such a huge weapon to the height required was beyond consideration at that time. This led Barnes Wallis to draw up a bomber sufficient to the job, the "Victory Bomber" of 50 tons which would fly at 320 mph at 45,000 feet carrying the bomb over 4,000 miles, but the Air Ministry were against a single bomb bomber and the idea was not pursued beyond 1942.

The Ruhr dams, though, were one of the strategic targets he had considered and Barnes Wallis was commissioned to develop a means of destroying them. Wallis's second paper, in 1942, had the title; Spherical Bomb — Surface Torpedo.

He had to make do with a maximum bomb size of 6 tons, and overcoming the problems of delivering the weapon to the target accurately led to the revolutionary "bouncing bomb", which utilised his massive contained blast idea but with water replacing the earth. The project distracted Wallis from his designs for a very large earth penetrating bomb until the successful use of the bouncing bombs by the Dam Busters in Operation Chastise which validated his ideas. The RAF still needed a bomb that delivered a single large blast and which could penetrate hardened targets like battle ships, bunkers and railway tunnels (a bunker buster), or to create a camouflet which would undermine foundations of structures like bridges causing them to collapse, and as the ability to lift 10 tons was still distant, Wallis was asked to consider what could be done with a smaller bomb and he worked on scaled down designs — one of which would become the 5 ton Tallboy.

The actual design and production of Tallboy was done without a contract on the initiative of a single official within the Ministry. As such the RAF were using bombs they had not bought and which were actually still the property of the manufacturers; Vickers. This situation was regularised once their capabilities were recognised.

Tallboys were used with great success against massive targets during the end phases of the war; targets which had been thought to be invulnerable to attack using conventional bombing techniques. Amongst many spectacular accomplishments, the attack on the V2 facility at Wizernes, France stands out. Here, a cupola roof designed to be absolutely bomb-proof was disrupted by Tallboy and Grand Slam hits undermining the foundations — a perfect vindication of Barnes Wallis' theories. In another attack on the Saumur tunnel, one Tallboy passed straight through the hill and exploded right inside the tunnel 60 feet below the surface.

Design

Most large Allied World War II aircraft bombs had very thin skins to maximise the weight of explosive which a bomber could carry — this was an improvement on the early part of the war when the actual HE content of British bomb designs was low. To be able to penetrate the earth (or hardened targets) without breaking apart the casing of the Tallboy had to be strong. Each was cast in one piece of high tensile steel that would enable it to survive the impact before detonation. At the same time to achieve the penetration required, Wallis designed the Tallboy to be very aerodynamic so that when dropped from a great height it would reach a velocity higher than traditional bomb designs. In the final design the tail of the bomb was about half the overall length of the finished weapon — the bomb casing was some 10 feet (3.05 m) of the overall 21 foot (6.35 m) length. Initially the bomb had a tendency to tumble, so the tail was modified — the fins were given a slight twist so that the bomb spun as it fell. The gyroscopic effect thus generated stopped the pitching and yawing, improved the aerodynamics and improved accuracy. The improved design worked so well that it was found in development that it passed through the sound barrier as it fell. When dropped from 20,000 ft (6,100 m) it made an 80 ft (24 m) deep crater 100 ft (30 m) across and could go through 16 ft (4.88 m) of concrete.

W. J. Lawrence wrote about the Tallboy bomb in his book, No 5 Bomber Group

It was an extraordinary weapon, an apparent contradiction in terms, since it had at one and the same time the explosive force of a large high-capacity blast bomb and the penetrating power of an armour-piercing bomb. On the ground it was capable of displacing a million cubic feet (29,000 m³) of earth and made a crater which it would have taken 5,000 tons of earth to fill. It was ballistically perfect and in consequence had a very high terminal velocity, variously estimated at 3,600 and 3,700 feet per second (1,100–1,130 m/s or about 2,500 mph), which was, of course, a good deal faster than sound so that, as with the V-2 rocket, the noise of its fall would be heard after that of the explosion.

However, according to other sources, the impact speed of the bomb was much slower at approximately 750 miles per hour. If air resistance is ignored, an upper limit to the impact speed can be estimated using the simple high school physics kinematic formula:

$\,\!v^{2}=u^{2}+2a\Delta s$

which yeilds a speed in agreement with the lower figure.

The weight of the Tallboy (approximately 12,000 lb.) and the high altitude required of the bombing aircraft meant that the Lancaster bombers used had to be specially adapted. Armour plating and even defensive armament were removed to reduce weight and the bomb-bay doors had to be adapted. Even then the Lancaster was not capable of reaching the bomb's intended dropping height of 40,000 ft (12,200 m) but only around 25,000 (7,700 m). At the same time No. 617 "Dambusters" Squadron trained in the use of a special bombsight the Stabilizing Automatic Bomb Sight (SABS). For accuracy multiple corrections had to be made for temperature, windspeed etc. However it was only effective if the target could be identified and several missions were cancelled or unsuccessful because of difficulty in accurately identifying and marking the targets.

Each bomb was a precision-built instrument of war made from expensive materials and carefully finished. They were not considered expendable and if not used on a raid were to be brought back to base rather than safely dropped in the sea. The value of the weapon offset the additional risk to the aircrew.

The Tallboy was used to attack strategic targets that could not be destroyed by other means. When it was found that the Lancaster could be modified to carry a bomb larger than the Tallboy, Wallis produced the even larger Grand Slam bomb.

Tallboy operations

• Saumur rail tunnel — The sole operational north-south route on the Loire. Nineteen Tallboy equipped, and six conventionally equipped Lancasters of No. 617 Squadron, attacked on the night of 8/9 June 1944. This was the first use of the Tallboy bomb and the line was destroyed — one Tallboy bored through the hillside and exploded in the tunnel about 60 ft (18 m) below, completely blocking it. No aircraft were lost during the raid.
• E-boat pens at Le Havre and Boulogne — On 14 June 1944 as part of the first massive RAF daylight raid since the end of May 1943, 22 Lancasters of 617 Squadron attack the concrete covered E-boat pens just before the first wave bombed. Several hits were scored on the pens and one bomb penetrated the roof. The E-boat pens at Boulogne were attacked the next day. The E-boats were targeted to prevent them attacking the Normandy invasion force.
• Eperlecques blockhouse in the woods at Watten, near St Omer — It was attacked by No. 617 Squadron on 19 June 1944. The nearest Tallboy bomb landed 50 yards (46 m) from the target. The target was attacked again on 27 July resulting in one hit which did not penetrate the structure
• La Coupole V2 rocket bunker at Wizernes — Bombed on 24 June 1944. No. 617 Squadron scored several hits with their Tallboy bombs and undermined the foundations but did not penetrate the concrete dome.
• Siracourt V-1 flying-bomb launch complex — The Lancasters of No. 617 Squadron scored 3 direct hits on the concrete structure with Tallboy bombs without loss on 25 June 1944.
• A railway tunnel at Rilly La Montage used as a flying-bomb store — On July 24 1944 both ends of the tunnel were collapsed by Tallboy bombs dropped by No. 617 Squadron.
• V-3 cannon installation at Mimoyecques — The German superguns were destroyed before they could be used against London by Tallboys dropped by 617 Squadron on 6 July 1944.
• U-boat pens at Brest etc. — on 5 August 1944, 15 Lancasters of No. 617 Squadron attacked the U-boat pens at Brest and scored 6 direct hits with Tallboys penetrating the concrete roofs. 1 Lancaster shot down by flak. Subsequent attempts to reinforce other sites with even thicker concrete diverted resources from other projects.
• Dortmund-Ems Canal near Ladbergen, north of Munster – No. 617 Squadron scored six direct hits with Tallboys on night September 23/24 1944.
• Kembs Dam north of Basle — The dam waters could have been kept in reserve to flood the area of a US advance. On 7 October 1944, the Dambusters destroyed the lock gates with Tallboys dropped at low level releasing the stored water.
• Sorpe Dam — This target of the original Dambusters raid survived a second attack by 9 Squadron on 15 October 1944 (617 Squadron did not participate in this raid). The Tallboy bombs were seen to hit the dam but did not breach it.
• The German battleship Tirpitz operations — The Tirpitz threatened the Arctic convoys to the USSR from her base in Northern Norway which was out of bombing range from British bases. No. 617 and No. 9 squadrons carried 24 Tallboys from Yagodnik near Archangel in Russia to attack the Tirpitz on the 15 September 1944. In the face of extensive flak and smoke cover they failed to sink the ship but damaged her so extensively that she was forced to head south to Tromsø fjord to be repaired. This fjord was in range of bombers operating from Scotland. She was unsuccessfully attacked in October from Lossiemouth base. Finally on 12 November 1944, the two squadrons attacked Tirpitz again and after three direct hits she capsized and sank.
• E-boat pens at IJmuiden — On 15 December, 1944 No. 617 Squadron attacked the pens with Tallboys, but smoke obscured the results.
• Urft Dam, (30 miles south west of Cologne) was attacked, on 8 December and 11 December 1944, to prevent it being used to flood the area below as American troops advanced. The lip of the dam was damaged, but the Germans prevented further damage by lowering the water level.
• Politz — attacked by No. 617 21 December 1944
• U-boat pens and shipping in Bergen — attacked by No. 617 and No. 9 squadrons with Tallboys on 12 January 1945. Three penetrated the 3½-metre-thick roof causing extensive damage at the cost of three Lancasters lost.
• U-boat pens at IJmuiden — attacked by No. 9 Squadron with Tallboys on 3 February 1945 hits were claimed and no aircraft were lost.
• U-boat pens at Poortershaven — attacked by No. 617 Squadron with Tallboys on 3 February 1945 hits were claimed and no aircraft were lost.
• U-boat pens at IJmuiden — attacked by No. 617 Squadron with Tallboys on 8 February 1945 with no aircraft lost.
• Bielefeld and Arnsberg viaducts — attacked by No. 617 and No. 9 squadrons with Tallboys and the first Grand Slam bomb on 14 March 1945. The Arnsberg viaduct withstood the attack but 100 m of the Bielefeld viaduct collapsed through the 'earthquake effect' of the Grand Slam and Tallboys.
• Arnsberg viaduct — attacked again on 15 March 1945 by No. 9 Squadron it did not collapse.
• Hamburg U-boat shelters — attacked on 9 April 1945 by No. 617 Squadron with Tallboys and Grand Slam bombs. Some of the bombs hit their target and no aircraft were lost.
• Pocket battleship Lützow — attacked on 16 April 1945 by No. 617 Squadron, despite intense flak 15 aircraft managed to bomb the target with Tallboys or with 1,000-pounders. One near miss with a Tallboy tore a large hole in the bottom of the Lützow and she settled to the bottom in shallow water. One Lancaster was shot down, the Squadron's last loss in the war.
• Coastal battery positions at Heligoland — attacked on 19 April 1945 by No. 617 and No. 9 squadrons armed with Tallboys. All the positions were hit and no aircraft were lost.
• Hitler's vacation home, Berghof, near Berchtesgaden — attacked on 25 April 1945 with a mixed force which included 6 Lancasters of No. 617 Squadron dropping their last Tallboys. The bombing appeared to be accurate and effective.

Vital statistics

Length	6.35 m (21 ft)
Diameter	950 mm (38 in)
Weight	5,443 kg (12,000 lb)
Warhead	2,358 kg (5,200 lb) "Torpex D1" (Torpedo explosive)
Number used	854[2]

References

• Barnes Wallis Trust
• English Bombs of WWII
• Bombs Weapons Rockets Aircraft Ordnance
• Spartacus: Tallboy

Further reading

• A picture of a Lancaster carrying a Tallboy