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
Designed1943
ManufacturerVickers, Sheffield
Clyde Alloy/Steel Company of Scotland, Blochairn, Glasgow
Produced1944–45
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]
Specifications
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)
Detonation
mechanism
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]

Development

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]