Grand Slam (bomb)

The Grand Slam was a 22000 lb 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, 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".

Development
On 18 July 1943, work started on a larger version of the Tallboy bomb, which became the Grand Slam. As with the original Tallboy, the Grand Slam's fins generated a stabilizing spin and the bomb had a thicker case than a conventional bomb, which allowed deeper penetration. After the hot molten Torpex was poured into the casing, the explosive took a month to cool and set. Like the Tallboy, because of the low rate of production and consequent high value of each bomb, aircrews were told to land with their unused bombs on board rather than jettison them into the sea if a sortie was aborted.

After release from the Avro Lancaster B.Mk 1 (Special) bomber, the Grand Slam would reach near-supersonic speed, approaching 1,049 ft/s (715 mph) - (320 m/s, 1150 km/h), and penetrate deep underground, with the explosion causing a camouflet (cavern) and shifting the ground to undermine a target's foundation.

Unlike the Tallboy, the Grand Slam had been designed to directly penetrate concrete roofs; they tended to not detonate prematurely nor break up. This made them far more effective than any existing bomb.

Grand Slam combat operations
By the end of the war, 42 Grand Slams had been dropped on active service.


 * 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 viaduct. More than 100 yards of the Bielefeld viaduct collapsed through the earthquake bomb effect of the Grand Slam and Tallboy bombs of No. 617 Squadron. No aircraft were lost.


 * 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.


 * Arnsberg, 19 March 1945
 * 19 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. The standing structure was severely damaged.


 * Arbergen, 21 March 1945
 * 20 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; 2 Tallboy hits caused sufficient damage to the approaches to the bridge to put it out of use. One 617 Lancaster was lost.


 * Nienburg, 22 March 1945: 20 Lancasters of No. 617 Squadron, six carrying Grand Slams, the remainder Tallboys, attacked the railway bridge at Nienburg, between Bremen and Hanover. 5 Grand Slams made direct hits and the bridge was completely destroyed. Another 5 bombs were brought home by the squadron.


 * Bremen, 23 March 1945
 * 20 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. Author Jon Lake claims instead that two Grand Slams struck the bridge.


 * Farge, 27 March 1945
 * 20 Lancasters of No. 617 Squadron attacked the Valentin submarine pens, a huge, nearly-ready structure with a concrete roof up to 23 ft (7.2 m) thick. Two Grand Slam bombs penetrated in parts of the pen with a 14 ft 5 inches (4.5 m) thick roof, which rendered the shelter unusable. No aircraft were lost.


 * Hamburg, 9 April 1945
 * 17 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.


 * Heligoland, 19 April 1945
 * 20 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.

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, 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.

Survivors
Four complete Grand Slam bombs are preserved and displayed in the United Kingdom at the RAF Museum, London, Brooklands Museum, RAF Lossiemouth and the Battle of Britain Memorial Flight Visitors' Centre at RAF Coningsby. The main portion of a bomb, without the lightweight tail, is at the Kelham Island Museum in Sheffield.

A live Grand Slam bomb was mistakenly displayed as a gate guardian at RAF Scampton for nearly fifteen years before the mistake was realised. It was gingerly removed (by crane and low-loader) to the test range at Shoeburyness, where it was detonated.

A T-14 bomb (an American-made variant of the Grand Slam) is displayed at the Air Force Armament Museum in the United States.

Two Grand Slam bombs are in Pakistan, one each in Karachi and Sargodha. The bombs were in India, probably in transit to the Pacific theatre, when the war ended and remained there to be inherited by Pakistan on its creation by partition from India in 1947.