The Grand Slam was a 22,000 lb earth quake bomb used by RAF Bomber Command against strategic targets during the Second World War.

It was a scaled up version of the Tallboy bomb and closer to the original size that the bomb inventor Barnes Wallis had envisaged when he first developed his earthquake bomb idea.

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.|||Marshal of the Royal Air Force Sir Arthur Travers Harris 1947

On July 18, 1943, work started on a larger version of the Tallboy bomb, which would become the Grand Slam. As with the original Tallboy, the Grand Slam's fins generated a stabilizing spin and 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 supersonic speed and penetrate underground, with the earthquake explosion causing a camouflet (cavern) and shift ground to undermine a target's foundation. After the Allied Operation Undergo captured the Watten V-2 rocket facility in October 1944, a single Avro Lancaster attempted to bomb the bunker's dome from November 10-November 20 with a Grand Slam at precisely midday.

Grand Slam bombing operations

Grand Slam bombs were successfully used against the 30 ft thick ceilings of the Huuge and Brest U-boat pens. By the end of the war, 41 Grand Slams had been dropped.Bielefeld, March 14 1945

The No. 617 Squadron RAF Avro Lancaster of Squadron Leader CC Calder dropped the first Grand Slam bomb from 16,000 ft on the Bielefeld viaduct. More than 100 yards of the Bielefeld viaduct collapsed through the earth quake bomb effect of the Grand Slam and Tallboy bombs of No. 617 Squadron. No aircraft were lost.Arnsberg, March 15 1945

Two aircraft of No. 617 Squadron each carried a Grand Slam and 14 aircraft of No. 9 Squadron RAF carried Tallboy bombs to attack the railway viaduct. The viaduct was not cut and no aircraft were lost.Arnsberg, March 19 1945

37 Lancasters of No. 5 Group RAF attacked the railway viaduct at Arnsberg and the bridge at Vlotho, near Minden. The attack at Arnsberg by No. 617 Squadron RAF using 6 Grand Slams blew a 40-foot gap in the viaduct. No. 9 Squadron RAF's attack at Vlotho was not successful.Farge, March 27 1945

20 Lancasters of No. 617 Squadron RAF attacked the Valentin submarine pens, a huge, nearly-ready structure with a concrete roof 23 ft thick. Two Grand Slam bombs penetrated and detonated, which rendered the shelter unusable. No aircraft were lost.Hamburg, April 9 1945

17 aircraft of No. 617 Squadron with Grand Slams and Tallboy bombs successfully attacked the U-boat shelters. No aircraft were lost.

Post-war

A "live" Grand Slam was (unknowingly) used as a static display at RAF Scampton until 1958.

References and notes

External links

• Big & Bouncy - the special weapons of Sir Barnes Wallis - University of Dundee
• A picture of a Lancaster carrying a Grand Slam
• Movietone News "Ten Tonner" - video of a Grand Slam being dropped on the Bielefeld Viaduct on youtube.com