On 13 March 1945 the largest bomb ever dropped by British forces, during WWII, was first tested ‘live’ in the New Forest at Ashley Walk Bombing Range.
The Grand Slam was a 22,000-lb MC high explosive deep-penetration bomb designed by Barns Wallis following on from his creation of the smaller Tallboy (a 12,000-lb MC deep-penetration bomb). Due to limited production and testing time the first test of this bomb used a live Grand Slam. The test range was Ashley Walk and it was dropped from a modified Avro Lancaster.
The bomb aimer sighted on the Ministry of Home Security Target, known locally as the ‘Sub Pen’, and due to their height and speed released the bomb whilst flying over Fordingbridge. The bomb then fell eventually hitting and exploding 100 yards from the target. The crater it made was 140 feet wide and 70 feet deep.
On impact the bomb would penetrate deep into the ground before exploding and could also penetrate reinforced concrete. The successful trail enabled the decision to be made in March 1945 to make 40 Grand Slam bombs and they were dropped on the V2 and V1 launching sites in the Netherlands as well as against viaducts, railway tracks (deep in tunnels) and U-boat Pens.
On this site the Ashley Range Overview page has links to pages about the other targets on the range.
Documents from the National Archives added:
“Tallboy” and “Grand Slam” bombs: Trials and development – 1944 Jan-1945 May
Former reference in its original department: IIH/258/1/157 5G/50/12
- 1945-03-07 – AIR 14-2011 – Estimated crater size and volume for “GRAND SLAM”
- 1945-03-12 – AIR 14-2011 – Grand Slam terminal velocity of 4,580 feet per second. (Note; no year is given on this document, but we suggest 1945)
- 1945-04-09 – AIR 14-2011 – Code name “GRAND SLAM” compromised. Grand Slam is to known as the 22,000lb M.C. and the Tallboy as 12,000lb M.C.