Grand Slam (bomb)
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Grand Slam Bomb

Grand Slam
British Grand Slam bomb.jpg
A Grand Slam bomb being handled at RAF Woodhall Spa
TypeEarthquake bomb
Place of originUnited Kingdom
Service history
In service1945
Used byRoyal Air Force
WarsWorld War II
Production history
DesignerBarnes Wallis
ManufacturerVickers, Sheffield
Clyde Alloy/Steel Company of Scotland, Blochairn, Glasgow
No. built42 used, 99 built by Clyde Alloy plus others from the Smith Corporation of America[1]
VariantsM110 (T-14) 22,000-lb GP Bomb (United States)[2]
Mass22,000 lb (10,000 kg)
Length26 ft 6 in (8.08 m)
 lengthTail 13 ft 6 in (4.11 m)
Diameter3 ft 10 in (1.17 m)

FillingTorpex D1
Filling weight4,144 kg (9,136 lb)
penetration: 40 m (130 ft) (earth)[3] 2-6 m (20 ft) (concrete)[3][4]
Blast yield6.5 tons TNT equivalent[a]

The Grand Slam was a 22,000 lb (10,000 kg) earthquake bomb used by RAF Bomber Command against strategic targets during the Second World War.

Known officially as the Bomb, Medium Capacity, 22,000 lb[b], it was a scaled-up version of the Tallboy bomb and closer to the original size that the bombs' inventor, Barnes Wallis, had envisaged when he first developed his earthquake bomb idea. It was also nicknamed "Ten ton Tess".[5]

It was previously the most powerful non-atomic aerial bomb ever used in combat. Currently, the most powerful non-atomic bomb, is the US GBU-43/B MOAB (21,600 lb) device used in a 2017 attack against ISIL forces in Afghanistan.[6]


When the success [of the Tallboy bomb] was proved, Wallis designed a yet more powerful weapon... This 22,000 lb bomb did not reach us before the spring of 1945, when we used it with great effect against viaducts or railways leading to the Ruhr and also against several U-boat shelters. If it had been necessary, it would have been used against underground factories, and preparations for attacking some of these were well advanced when the war ended.

-- Sir Arthur Harris (1947).[7]
Grand Slam bomb casings awaiting delivery

On 18 July 1943, work started on a larger version of the Tallboy bomb, which became the Grand Slam.[2] As with the original Tallboy, the Grand Slam's fins generated a stabilizing spin[8] and the bomb had a thicker case than a conventional bomb, which allowed deeper penetration. Unlike the Tallboy, the Grand Slam was originally designed to penetrate concrete roofs.[9] Consequently, it was more effective against hardened targets than any existing bomb.

Grand Slam bomb exploding near Arnsberg viaduct 1945

After release from the Avro Lancaster B.Mk 1 (Special) bomber,[2] the Grand Slam would reach near-supersonic speed, approaching 1,049 ft/s (320 m/s), 715 mph (1150 km/h). When it hit, it would penetrate deep underground before detonating. The resulting explosion could cause the formation of a camouflet[10] (cavern) and shift the ground to undermine a target's foundation. The Grand Slam was so heavy that the Lancaster's wingtips bent upwards by six to eight inches (150 to 200 mm). When the bomb was dropped, the plane leapt up 200 to 300 feet (61 to 91 m).[11]

The first Grand Slam was tested at the Ashley Range in the New Forest, on 13 March 1945.[12]

Like the Tallboy, after the hot molten Torpex was poured into the casing, the explosive took a month to cool and set. Therefore, the Grand Slam had a low rate of production and consequent high value for each bomb. As a result, aircrews were told to land with their unused bombs on board rather than jettison them into the sea if a sortie was aborted.[13] If returning with an undropped bomb, the bomber had to divert from Woodhall to Carnaby which had a longer runway.[11]

Grand Slam combat operations

A 617 Sqn Lancaster dropping a Grand Slam bomb on the Arnsberg viaduct, March 1945.
The damage caused by one of the two Grand Slams that exploded in the roof of the Valentin submarine pen, 27 March 1945; a figure stands at the edge of the rubble pile, providing a sense of the scale of the damage
An RAF officer inspects the hole left by a 'Grand Slam' bomb which exploded in the reinforced concrete roof of the German submarine pens at Farge, north of Bremen, Germany. This was the result of a daylight raid by 18 Avro Lancasters of No. 617 Squadron RAF on 27 March 1945. Two direct hits by 'Grand Slams' caused sections of the partially-completed roof to collapse

By the end of the war, 42 Grand Slams had been dropped in active service:[14]

Bielefeld, 14 March 1945

The No. 617 Squadron RAF Avro Lancaster of Squadron Leader CC Calder dropped the first Grand Slam bomb from 11,965 ft (3,647 m) on the Schildesche (or Bielefeld) viaduct. [15] A large section of the viaduct collapsed [16] from the earthquake bomb effect of the Grand Slam and Tallboy bombs of No. 617 Squadron. No aircraft were lost.[17] Previously by mid-March over 3,500 tons had been dropped on the viaduct in 54 attacks, but the viaduct was still standing. Damage from 17 hits in one raid was repaired in 24 hours. After this raid, seven arches incorporating 200 feet (61 m) of the northern span and 260 feet (79 m) of the southern span had been obliterated.[18]
Arnsberg, 15 March 1945
Two aircraft of No. 617 Squadron RAF each carried a Grand Slam and 14 aircraft of No. 9 Squadron RAF carried Tallboy bombs to attack the railway viaduct in poor weather. One Grand Slam and 10 Tallboys were dropped, while one of the Lancasters was forced to bring its bomb back. The viaduct was not cut and no aircraft were lost.[17][19][20]
Arnsberg, 19 March 1945
Nineteen Lancasters of No. 617 Squadron, six carrying Grand Slams, the remainder Tallboys, attacked the railway viaduct at Arnsberg. All Grand Slams were dropped and blew a 40-foot (12 m) gap in the viaduct.[17][21] The standing structure was severely damaged.[20] There was a whole school under the arches, and those in it were all suffocated.[22]
Arbergen, 21 March 1945
Twenty Lancasters of No. 617 Squadron, two carrying Grand Slams, the remainder Tallboys, attacked the railway bridge at Arbergen. The Grand Slams landed off target due to heavy flak and aiming problems; two Tallboy hits caused sufficient damage to the approaches to the bridge to put it out of use. One 617 Lancaster was lost.[23]
Nienburg, 22 March 1945
Twenty Lancasters of No. 617 Squadron, six carrying Grand Slams, the remainder Tallboys, attacked the railway bridge at Nienburg, between Bremen and Hanover. One Grand Slam and two Tallboys made direct hits and the bridge was destroyed. The remaining five Grand Slams were brought home by the squadron.[20][24]
Bremen, 23 March 1945
Twenty Lancasters of No. 617 Squadron, six carrying Grand Slams, the remainder Tallboys, attacked a railway bridge near Bremen. The Grand Slams appear to have landed too far from the target, which was brought down by a Tallboy.[25] Author Jon Lake claims instead that two Grand Slams struck the bridge.[20]
Farge, 27 March 1945
Twenty Lancasters of No. 617 Squadron attacked the Valentin submarine pens,[4] a huge, nearly-ready structure with a concrete roof up to 23 ft (7.2 m) thick. Two Grand Slam bombs hit the pen, failing to penetrate a 14 ft 5 inches (4.5 m) thick roof but causing large holes by exploding within the concrete.[4][26] No aircraft were lost.[17][27]
Hamburg, 9 April 1945
Seventeen aircraft of No. 617 Squadron, two with Grand Slams and the remainder with Tallboy bombs successfully attacked the U-boat shelters. The Grand Slams appear to have missed, but six Tallboy hits caused considerable damage. No aircraft were lost.[28][29]
Heligoland, 19 April 1945
Twenty aircraft of No. 617 Squadron, six with Grand Slams and the remainder with Tallboy bombs, along with 16 aircraft from No. 9 Squadron, attacked coastal gun-batteries. No aircraft were lost.[28][30]

Post-war operations

Beginning in March 1946, Project Ruby was a joint Anglo-American project to investigate the use of penetration bombs against heavily protected, concrete targets. The target selected was the Valentin submarine pens near Bremen, that had been rendered unusable and abandoned since 617 Squadron's attack on 27 March 1945. Grand Slams were carried by Lancasters from No. 15 Squadron RAF and US Boeing B-29 Superfortress. Around 140 sorties were flown, testing a range of different bombs including the rocket-assisted Disney bomb.[31][3]


A Grand Slam bomb at the RAF Museum, London

Five complete Grand Slam bombs are preserved and displayed in the United Kingdom at the RAF Museum, London; Brooklands Museum; RAF Lossiemouth; Dumfries and Galloway Aviation Museum and the Battle of Britain Memorial Flight Visitors' Centre at RAF Coningsby. Main portions of these bombs, without their lightweight tails, can be seen at the Kelham Island Museum in Sheffield and Yorkshire Air Museum at Elvington.

The T-14 bomb is an American-made variant of the Grand Slam;[31] one is displayed at the Air Force Armament Museum in the United States.

See also


  1. ^ Torpex is 50% more powerful than TNT. Truman described the Little boy bomb (yield > 13 kilotons) against Hiroshima in terms of the Grand Slam: "...more than two thousand times the blast power of the British Grand Slam" (Truman 2008).
  2. ^ "Medium capacity" refers to the ratio of bomb case to explosive filling; in the case of the Grand Slam, this was less than 50 percent explosive by weight, in contrast to "high capacity" bombs like the Blockbuster bombs, which contained up to three-quarters of their weight in explosive.


  1. ^ Flower 2004, appendix 4 "bombs":
  2. ^ a b c (Godwin 2007)[unreliable source]
  3. ^ a b c Flight staff 1946.
  4. ^ a b c Grube 2006.
  5. ^ MAP Exhibition Flight 21 June 1945 p688
  6. ^ Cooper, Helene; Mashal, Mujib (13 April 2017). "U.S. Drops 'Mother of All Bombs' on ISIS Caves in Afghanistan". The New York Times. Archived from the original on 14 April 2017. Retrieved 2017.
  7. ^ Harris 2005, p. 252.
  8. ^ Constable 2008.[unreliable source]
  9. ^ Flower 2004, p. 375.
  10. ^ Kharin, Kuzmina & Danilova 1972.
  11. ^ a b Nichol 2015, pp. 296,298.
  12. ^ "Ashley Range". New Forest National Park. Retrieved 2014.
  13. ^ Flower 2004, p. 335.
  14. ^ Flower 2004, Appendix 4.
  15. ^ Flower 2004, p. 331.
  16. ^ "Ten Tonner". Movietone News. Retrieved 2010 – via video of a Grand Slam being dropped on the Bielefeld Viaduct
  17. ^ a b c d RAF staff 2005, March
  18. ^ Nichol 2015, pp. 292,293,299.
  19. ^ Flower 2004, pp. 332-334.
  20. ^ a b c d Lake 2002, p. 62.
  21. ^ Flower 2004, pp. 334-40.
  22. ^ Nichol 2015, p. 301.
  23. ^ Flower 2004, pp. 340-42.
  24. ^ Flower 2004, pp. 342-43.
  25. ^ Flower 2004, pp. 344-47.
  26. ^ RAF staff 2005a, Grand Slams.
  27. ^ Flower 2004, pp. 348-52.
  28. ^ a b RAF staff 2005, April
  29. ^ Flower 2004, pp. 355-58.
  30. ^ Flower 2004, pp. 362-64.
  31. ^ a b Comparative Test of the Effectiveness of Large Bombs Against Large Reinforced Concrete Structures (PDF), AAF Proving Ground, Eglin Field, Florida, 31 October 1946


External links

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