Grand Slam Bomb

Grand Slam Bomb

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Most bombs dropped from aircraft during the Second World War ranged from 100lb to 4,000lb in weight. Barnes Wallis carried out experiments in developed much larger bombs and eventually he produced Tallboy, a bomb that weighed 12,000lb. This bomb, also known as the earthquake bomb,was successfully used against V1 Flying Bomb launch sites and in the sinking of Germany's giant battleship, Tirpitz, on 12th November, 1944.

In 1945 Barnes Wallis developed the 22,000lb Grand Slam. This bomb was so heavy it could only be carried by a specially adapted Avro Lancaster. The first one was dropped on Germany on 14th March, 1945.

We already had Wallis's 12,000 Ib. medium capacity bomb, which was capable of breaking through the roof of a railway tunnel or a very thick concrete roof, and when the success of this bomb was proved Wallis designed a yet more powerful weapon, the 22,000 Ib. bomb, the most destructive missile in the history of warfare until the invention of the atom bomb. This 22,000 Ib. 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.

The original design plans are important, and these were for a bomb designed to use the earth underground as a shockwave transmission medium. This scomes form the paul brickhill book on the dambusters.

"The design was very aerodynamic with a tail which caused it to spin. This allowed it to break the sound barrier as it fell."

How? - Omegatron 03:16, Apr 25, 2005 (UTC)

No expert on aerodynamics, but I'd take a guess there are two factors. Firstly, and most importantly, the spin produces a gyroscopic effect so that the bomb is kept upright as it falls. If this did not happen then the very high turbulence experienced as the speed of sound is approached would cause the bomb to tumble off its axis and to slow. Secondly, I think the spinning will probably produce some sort of effect around the bomb that will reduce the resistance to the fall. That second point may be wrong, though.

Your second point is incorrect, I think, but you're spot on wit hthe first. To say "it allowed" it to break the sound barrier is a little misleading, though, since the spinning slowed the bomb directly (resistance with the air is used to produce rotational motion), but the consequences of that spinning (not tumbling as it falls, as well as being less vulnerable to drafts and breezes) would probably improve the top speed. Of course, it it was dropped in dead air and from a stationary position such as a tower or zeppelin, it would fall faster with regular flights. This is an unliekly situation, so I'll exclude it for now. Oceanhahn 05:29, 25 May 2006 (UTC)

The article also quotes 2,358kg of explosive, the same number as for the Tallboy bomb. Is that right?

Grand Slam contained approx 9,200 lb of Torpex. Tallboy, 5,200 lb. — Preceding unsigned comment added by (talk) 11:50, 20 February 2015 (UTC)

As so often, regarding the Valentin submarine pens, the german article claims they only had 5 metres thick roofs and the Grand Slam bomb could not break through them (and the RAF website times out). -- Darklock 00:55, 26 June 2006 (UTC)

This is a bit misleading. It reads as if this description relates specifically to the Grand Slam, but most of it also features in the Tallboy article. TheMadBaron 09:27, 13 August 2005 (UTC)

keep separate as different weapons with different missions. GraemeLeggett 20:06, 13 August 2005 (UTC)

They are different bombs. If we merge these, then we must merge Fat Man and Little Boy to be consistent. Does not compute./ Moriori 22:18, August 13, 2005 (UTC)

Not a good analogy: those used radically different bomb architecture (plutonium/implosion and uranium/gun), while Grand Slam was just an upsized version of Tallboy. Try the .50 calibre round and .30-06. Virtually the same, except one is larger. Should they be merged? Moriori 19:43, August 14, 2005 (UTC) Was one literally an adaptation of the other, a development by the same designer? I haven't said Grand Slam and Tallboy should be merged, just that the duplication because of common origin should be snipped. Tearlach 23:50, 14 August 2005 (UTC) Yes, I think one would have been literally an adaptation of the other, but I don't know which was chicken or egg. ):- Moriori 00:00, August 15, 2005 (UTC) I'd say keep them separate, but cut the duplicated material in Grand Slam and refer to Tallboy for the general background principles. Tearlach 19:04, 14 August 2005 (UTC)

Keep then seperate do not cut the duplicate material as it is not a lot and was true for both bombs. It is not as if it uses either a lot of disk space, bandwidth or screen space. PBS 00:47, 1 September 2005 (UTC)

Also the paragraph mentions the only type of British bomber which could carry the Grand Slam.I have also mentioned that the fist use against the enemy involved destroying the foundations by a proximity drop not a direct hit. PBS 01:19, 1 September 2005 (UTC)

I don't think that tagging on to the bottom of this page, "the US developed an even bigger bomb"(that was never used operationally)serves any useful purpose. I'll remove it unless some one can justify it's relevance. Uncool 1 17:44, 25 September 2005 (UTC)

See RAF_Scampton for a short bit on the last Grand Slam to be detonated after it was discovered that one loaded with torpex had been put on display as a gate guardian at the airbase.

The source for this story doesn't give a reference, and the paragraph in question begins "Apparently. ", so I'm not sure how much credence should be given to it.VirtualDave (talk) 09:17, 20 October 2008 (UTC)

The Bombs did not hit that part of the Pen with the 7 m roof as the text seems du say. So the Grand Slams "only" penetrate 4,5 m of concrete (as the subtitle of the Pcture correctly sais)--WerWil 20:19, 31 August 2006 (UTC)

Source? --PBS 18:36, 6 April 2007 (UTC)

I know only german sites: [1][2] --WerWil 17:40, 7 April 2007 (UTC)

The development history section says both that the grand slam would detonate "some 30m" below the ground and "over 40m". What is the real fact here? I imagine it is a fuzzy range and dependant on the ground material but please. --Lomacar 18:57, 22 September 2006 (UTC)

< After the Allied Operation Undergo[8] captured the Watten V-2 rocket facility in October 1944, a single Avro Lancaster attempted to bomb the bunker's dome from 10 November-20 November with a Grand Slam at precisely midday.[9] >

This is impossible to believe and should in my view be deleted. The first, trial, drop of a Grand Slam was not until 13th of March 1945. —Preceding unsigned comment added by (talk) 02:33, 18 October 2010 (UTC)

Deleted. (talk) 22:56, 31 October 2010 (UTC)

The article says: "A live Grand Slam bomb was accidentally displayed as a gate guardian at RAF Scampton for over a decade before the mistake was realised. It was gingerly removed (by crane and low-loader) to the test range at Shoeburyness, where it was detonated.[25]"

I'm not sure what "live" means. Does this mean it contained a charge or was it also armed with detenators? (talk) 11:47, 12 March 2012 (UTC)

It almost certainly means the former, i.e., containing explosive but un-fuzed. Non-'live' munitions usually are empty cases or contain an inert filling. The arming pistols would have been inserted into the tail pockets upon bombing-up shortly before flight, so unless the bomb had been loaded onto an aircraft and the operation then subsequently cancelled, it is unlikely that the bomb had ever been fuzed. So it was probably 'safe-ish' while a gate guard. Grand Slams were built in relatively small numbers and so it is likely that very few 'practice' examples (used for ballistics testing and for armourers' training) were made, at least before 1945. Hence the likelihood of the Scampton example being the 'genuine article'. A bomb is said to be 'live' when it contains explosives but is un-fuzed. When fuzed and ready to go it is said to be 'armed' - that's why the detonators/fuzes are also sometimes called 'arming pistols', especially in the navy. BTW, the term 'pistol' used for a detonator comes from the times when to scuttle a ship a barrel of gunpowder was stowed below decks and then detonated by a flintlock pistol fired by a long string tied to the trigger. — Preceding unsigned comment added by (talk) 14:50, 21 October 2012 (UTC) Is the Australian Armourers Association article reliable? See for a discussion. cmɢʟee୯ ͡° ̮د ͡° ੭ 18:52, 16 May 2013 (UTC)

Just curious - if this was the biggest bomb around, why was its official name 'Bomb, Medium Capacity'? Were there plans for something even bigger? (talk) 13:36, 1 February 2014 (UTC)

Medium Capacity refers to the ratio of bomb case to explosive filling, not the absolute size of bomb . See Blockbuster bomb for British "High Capacity" bombs. this website has articles on the various bombs. GraemeLeggett (talk) 13:55, 1 February 2014 (UTC) I went ahead and incorporated this as a parenthetical footnote in the main body of the article (and also in the article on the Tallboy). (talk) 18:54, 14 March 2019 (UTC)

The sentence: "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" even though there is a source, is incorrect.

The undercarriage is only designed to take the stresses of landing a Lancaster 'dry' ie without its bomb load. Hence an unused Grand Slam bomb would have to be jettisoned before attempting a landing otherwise the landing gear would collapse with the additional weight of c10 metric tonnes of Grand Slam. 2A02:8420:4AAD:AE00:70DA:2812:19DB:AFF0 (talk) 10:14, 14 March 2015 (UTC)

No. The Lancaster B.I Special had the undercarriage reinforced precisely so that it could land with the bomb still on board.Khamba Tendal (talk) 17:20, 25 August 2015 (UTC)

The sentence: "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" even though there is a source, is incorrect.

The undercarriage is only designed to take the stresses of landing a Lancaster 'dry' ie without its bomb load. Hence an unused Grand Slam bomb would have to be jettisoned before attempting a landing otherwise the landing gear would collapse with the additional weight of c10 metric tonnes of Grand Slam. Boatman (talk) 10:21, 14 March 2015 (UTC)

617 Squadron by Osprey disagrees. It's amazing what aircraft and crews can do if the motivation is there. GraemeLeggett (talk) 12:42, 14 March 2015 (UTC) Quite so. The stresses on landing need be no greater than those on take off, it depends on the skill of the pilot to be able to touch down gently enough and to allow the wings to gently unload the weight to the wheels. The stopping distance will also be greater, so a runway of adequate length is required. For a ham-fisted one the comment would otherwise be true. If an undercarriage will support a weight on take-off, it will also support the same weight on landing, but many pilots will not be able to touch down gently enough for this to be advisable, perhaps due to lack of skill, weather, etc,. Hence recommended maximum landing weights. — Preceding unsigned comment added by (talk) 16:49, 18 April 2016 (UTC) No, safe take-off weight and safe landing weight are not the same, the downward velocity of the aircraft on landing imposing a greater load. And, as I noted above, the Lancaster B.I (Special) was specifically adapted to land with the Grand Slam on board if necessary, owing to the exceptionally high cost of the bomb. Safe landing weight for the standard Lancaster was 55,000 lb. (Air Publication 2062A, Pilot's and Flight Engineer's Notes: Lancaster I, III & X, Air Ministry May 1944, p.29.) The aircraft had an empty weight of 31,242 lb and a tare weight with fixed military load of 35,831 lb. In 1945 it was rated for a maximum operational load (crew, fuel, oil, ammunition and bombload) of 36,169 lb, making for an all-up take-off weight of 72,000 lb. (Harry Holmes, Avro Lancaster, Airlife 2002, ISBN 1 84037 376 8, table p.79. The author spent his career with A.V.Roe & Co. and British Aerospace.) I don't know the exact figures for the B.I (Special), but its empty weight and tare weight were reduced by several thousand pounds compared to the standard Lancaster because the front and mid-upper turrets, the outer wing tanks and the bomb doors were all deleted. The safe landing weight was increased by the fitment of the reinforced undercarriage. The standard B.I could land at almost 20,000 lb above tare weight about 1,000 lb would be crew and most of the rest would be fuel and ammunition. The B.I (Special), being much lighter and fitted with a tougher undercarriage, would have a considerably larger margin, allowing it to land with a 22,000 lb Grand Slam as long as enough fuel had been burned off or jettisoned. Crews of 617 Squadron did in fact land back with Grand Slams still aboard on a number of occasions. Notably, five crews brought their Grand Slams back to Woodhall Spa after the Nienburg raid of 22 March 1945. Twenty Lancasters launched, six with Grand Slams and fourteen with Tallboys, to destroy a rail bridge near Bremen, but the CO, Wg Cdr JE Fauquier DSO** DFC, ordered just four crews to attack -- with one Slam and three Tallboys -- while the rest circled in reserve. The Slam and two Tallboys scored direct hits, destroying the bridge, so all the other bombs were returned to store. (Paul Brickhill, The Dam Busters, Pan 1983, ISBN 0-330-37644-6, p.257 Jon Lake, Lancaster Squadrons 1944-45, Osprey 2002, ISBN 978 1 84176 433 7, p.60.) Khamba Tendal (talk) 17:48, 23 June 2019 (UTC)

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CE, added references, citations, homogenised citation style. Auto edded and rm dupe wikilinks Keith-264 (talk) 22:03, 12 November 2019 (UTC)

Added more detail but wonder if anyone has Flower, Stephen (2004). Barnes Wallis' Bombs: Tallboy, Dambuster & Grand Slam? Cooper gets a little vague about which hits were Slams and which were Tallboys. Regards Keith-264 (talk) 23:29, 19 November 2019 (UTC)

It mentions the difference between GP and MC many times, word for word. — Preceding unsigned comment added by 2A02:2788:1008:2C3:E2CB:4EFF:FE88:1A2C (talk) 07:12, 27 January 2020 (UTC)

Ashley Walk Bombing Range

The former Ashley Walk Bombing Range lies to the north west of the New Forest, one of its more remote areas of open heath land where rare birds nest and ponies graze largely undisturbed. It is also one of the few places in the Forest where you can lose the sound of traffic from the trunk roads that bisect it. However, this scene of rural tranquility was not always the case.


Lancaster releasing Grand Slam – Imperial War Museum

During the early stages of the Second World war late in 1939 the New Forest Verderers considered a proposal to allow a temporary bombing range to be located south of the B3078 Fordingbridge to Cadnam road near Godshill. Its remoteness was considered ideal for the purpose with only small pockets of habitation in its immediate vicinity. Whilst we tend to think of everyone pulling together for the war effort, the location of the range was not universally popular with local people and landowners. Various letters were exchanged with the Air Ministry most of which were suggesting alternative sites in other parts of the country with one gentleman even suggesting Lundy Island in the Bristol Channel. In addition the Godshill Defence Committee was formed to voice their opposition – it appears that some things in the Forest never change!. However, the Verderers approval was eventually forthcoming in July 1940 after much deliberation, subject to the whole 5000 acre site being ring fenced to prevent Commoners animals straying onto the range. Only three houses had to be evacuated to accommodate the range which was encircled with nine miles of security fencing. It was accessed through any of thirteen gates positioned around the perimeter with the main entrance being near Godshill cricket pitch – it became the top secret Ashley Walk Bombing Range.

WW2 Bomb sizes – Grand Slam (top right) above Tallboy

Ashley Walk Bombing Range was under the direct control of RAF Boscombe Down near Amesbury, Wiltshire which was home to the Aeroplane and Armament Experimental Establishment (A&AEE). The A&AEE was transferred to this location at the outbreak of war in 1939 from its previous base at Martlesham Heath in Suffolk where it was feared that its position on the east coast would make it an easy target for German Bombers. The Boscombe Down unit became operational on 20 September 1939 but it lacked access to ranges to test the weapons it was developing and hence the need for the range at nearby Ashley Walk. While many other ranges were established across the UK, the range at Ashley Walk with its link to the A&AEE is thought to have been unique in that it was used predominantly to test weapons rather than for training purposes of bomber crews.

At the start of the Second World War , British bomb technology had not really progressed a great deal since the end of the Great War in 1918 when a 20lb bomb was considered large. Against this background there was an arms race to catch up with the perceived superiority of the German Luftwaffe and the weaponry that they had at their disposal. As a result, over the next five years this tranquil part of the New Forest would have more armaments dropped on it and fired at it that most other parts of England, with the exception of the larger cities – this included the largest ever bomb to be dropped on British soil.

This was wartime when “careless talk cost lives” and whilst some local lads managed to get onto the site from time to time, the general public had little idea what was going on behind the security fence. It was really not until the latter years of the 20th century that more facts about the range started to emerge as a result of work by local historians, most notably the publication “Ashley Walk – Its Bombing Range, Landscape and History” by Anthony Passmore and Norman Parker which is recommended for more detailed information on the subject. Unfortunately, because of the secret nature of its work very little photographic evidence of wartime operations on the range is available to us.


Scattered across Ashley Walk Bombing Range were a variety of specialist targets against which a rapidly improving armoury of new weapons were tested. Anything and everything capable of aerial delivery was tested here with the exception of incendiaries in view of their fire risk to the heath. These targets included the following:-

Air to Ground Targets – Situated to the west of the range and used for gun and rocket fire.

Fragmentation Targets – Situated in two separate areas on the range with one being used to test the protection afforded by aircraft pens (12 pens of British design and 12 of German design) and the other used to test fragmentation bombs against artillery.

Line Target – This was a 2000 yard track constructed of chalk resembling a railway line. Most of it is still clearly visible today.

Wall Targets – These 3 targets were imposing reinforced concrete structures of varying heights and their principal use was to test the strength of bomb casings (inert bombs of similar weight to primed bombs were used in these tests).

The picture below shows a Mosquito Bomber approaching the range between No.1 and No.2 Wall Targets.

The following picture shows No.3 Wall Target with a prototype “Highball” bomb heading in its direction from left to right. This target was quite different to the other two wall targets in its design. It was just under 9′ high, 20′ long and 6′ in depth, faced with armour plating.

Ship Target – A large rectangular steel target made of half inch thick steel plates used to test the penetrating powers of weapons designed for used against shipping. Unfortunately, no photographs remain of this target.


Low quality image of target shortly after construction

Ministry of Home Security Target – This latter target is perhaps the most interesting as for many years it has been known as the “Submarine Pens”. Due to the previous absence of records concerning the true nature of this building the common perception was that it was built to replicate the German submarine pens built along the Atlantic coast of France in order to test various weapons designed to destroy them. It comprised of a large reinforced concrete slab measuring 79 x 70 feet and 6 feet thick supported by five internal walls which were 6 feet high. Both front and rear ends were left open. The total volume of concrete in the target was 1643 cubic yards and the total weight of steel used was 121 tons of which 102 tons were reinforcing bars.

The work on this target commenced in February 1941 and was completed by September. Following completion a number of unsuccessful attempts were made to score a direct hit, and it was not until May 1943 that this was achieved by a USAAF Flying Fortress on their 15th attempt!

The photograph below shows the area as it is today.

However, this ‘sub pen’ theory is pure conjecture and any resemblance of the structure to actual U Boat pens is purely superficial. Even the smaller of the German buildings had far more substantial roofs, often with a void between concrete slabs to increase the resistance to bombs. Documents recently obtained from the National Archives describe the structure as a full size bomb resistant air raid shelter built by the Ministry of Home Security (department established in 1939 to direct national civil defence – primarily air-raid defences) in order to test its performance against the results obtained by laboratory tests on models. The following images show the interior of the structure and the damage done by bombs prior to it being covered with soil at the end of the war.

Ashley Walk Bombing Range tests on this target included both British and German bombs of various sizes which damaged the structure and these tests concluded in May 1943 after which it was used by the RAF for general bombing practice. More detailed information on the structure following research undertaken by local historian, Henry Cole can be obtained by clicking here.

To the south of the range, a concrete directional arrow (pictured below) can still be found on the left of the cycle track that leads from Fritham to Frogham. This was also the site of the Main Practice Tower and part of its concrete base remains visible. The arrow pointed to the Illuminated Target which lay in the valley below at Lay Gutter.

Directional Arrow pointing towards Illuminated target


Whilst inert bombs were dropped on the range to test their casings upon impact, a high volume of live bombs was also dropped over the area, many of which were leading edge technology in their time. One person whose name was synonymous with bomb technology was Sir Barnes Wallis and he was known to visit the range from time to time to witness the effectiveness of his inventions. Perhaps the most memorable of these was the Upkeep Mine, more commonly known as the “bouncing bomb”.

After the successful raids on the Möhne and Eder dams in the Ruhr Valley, Germany by the Lancaster bombers of 617 Squadron (“Dambusters” Squadron) in May 1943 attention was turned to other possible uses for the bouncing bomb principle. The Upkeep mines that were used to great success in these raids were cylindrical in shape and rotated in an anticlockwise direction so that they travelled down below the water surface when they hit the dams. It was thought that if they changed the direction of rotation it would roll up a beach and destroy coastal defences if dropped in the sea.

After concluding their trials at Boscombe Down and with Barnes Wallis watching from the ground, a group of five Lancasters of 617 Squadron loaded with inert versions of these revised Upkeep bombs approached Ashley Walk on 4 August 1943 to drop their payloads flying at very low level against a canvas screen target. While one aircraft’s bomb failed to release, the other four were dropped successfully and ran 1100 yards to the target. The following day five more aircraft of from 617 Squadron flew to the range to release inert versions against one of the concrete targets. Unfortunately, flying in close formation, the last of the planes to run at the target was affected by turbulence from the slipstream of the previous aircraft with the result that its wing clipped the ground and it crashed nose first and slid across the ground before bursting into flames. Fortunately its crew had a miraculous escape and lived to tell the tale although the bomb aimer suffered serious head injuries and never flew again. Despite the tests being deemed satisfactory it was decided not to use Upkeep over land following these tests and the project was eventually shelved.

Another Barnes Wallis variation of these bouncing bombs was the Highball which was a spherical bomb designed to bounce across the water to attack enemy shipping. It was tested at several locations including Ashley Walk when a Mosquito bomber proved that it could withstand heavy impact after making a number of Highball drops with inert versions at different angles against No.3 Wall. In order to determine whether the successful results achieved at Ashley Walk could be replicated under operational conditions, further trials were conducted at Loch Striven in February 1944, with Queen Elizabeth class battleship HMS Malaya acting as the target. However, despite a long period of testing it never proved successful and this idea was also shelved and never used in action during the war.

The following video clip shows a Mosquito Bomber releasing “Highball” bombs during a series of runs at the Ashley Walk Bombing Range. The Mosquito is flying over Wall No.1 and Wall No.2 before releasing inert versions of the bomb to test the strength of it’s casing against No.3 Wall. The clips show impact against No.3 Wall from a side view and also a frontal view. It is also interesting to note the close proximity of some of the observers.

Other of Barnes Wallis’ most potent weapons were successfully tested at Ashley Walk. Traditional bombing raids on large concrete structures in industrial Germany and fortifications along the French coast had not been particularly successful despite repeated attempts and it was against this background that Barnes Wallis developed the principle of an “earthquake” bomb capable of penetrating the earth or any structure before detonating. Their casings had to be hard enough to survive the initial impact when it penetrated the target prior to explosion seconds later. These bombs had to carry high payloads dropped from very high altitudes and because of the intricacies of their design each was virtually handmade. The first to emerge was the 12000lb “Tallboy” which, after an initial test at Ashley Walk on the night of 8/9 June, was hastily and successfully deployed the following day by 617 Squadron on the Saumur railway tunnel, 125 miles south of the battle that was raging on the Normandy beaches. These bombs continued to be used during the Allied invasion of Europe against heavily fortified German bunkers and U Boat pens. It was also a Tallboy that sunk the Tirpitz, the pride of the German Baltic fleet.

Grand Slam crater with “sub pens” top left

In view of the precision required in their aerial delivery, these bombs were entrusted to 617 (Dambusters) Squadron whose Lancasters had to be specifically modified to carry them. Encouraged by early Tallboy testing, Barnes Wallis turned his attention to an even bigger “earthquake” bomb which became known as Grand Slam. This was a 22000 lb bomb that was also nicknamed “Ten Ton Tess”. A live version was only tested once on UK soil – in the middle of Ashley Walk range. On 13 March 1945 a specially modified Lancaster flying at 16000 feet released Grand Slam over Godshill. Barnes Wallis and many other officials were at the range to witness this live test. After it buried itself in the ground upon impact, they started counting. On nine seconds, the blast was minimal but villagers felt the earth shake for miles around and it produced an enormous crater around 130 feet in diameter and over 70 feet deep just to the north west of the Ministry of Home Security target. To this day it remains the largest ever explosion from a bomb dropped on British soil. The crater can be seen in the bottom of the picture below with the “sub pens” top left.

When news of the successful reached 617 Squadron, two Lancasters flown by the CO Group Captain J.E ‘Johnny’ Fauquier and Squadron Leader Charles ‘Jock’ Calder took off from Woodhall Spa both loaded with a Grand Slam. They required the entire length of the runway to become airborne and headed straightaway for the Bielefeld Viaduct in Germany but due to heavy cloud over the area they were forced to return to base with their bombs intact.

Grand Slam bomb loading at Woodhall Spa – Imperial War Museum

The raid was rescheduled for the following day, 14th March 1945, and at 1.00pm the same two pilots prepared to take off again from their base for the Bielefeld viaduct. The rest of the squadron (14 aircraft) were fitted with Tallboy bombs. Unfortunately, bad luck struck the CO’s Lancaster even before it left the ground when a mechanical fault caused one of the engines to shut down leaving just one Grand Slam fitted to Calder’s aircraft for the raid. Seeing Fauquier’s Lancaster with with its engine problem and the figure of his CO racing towards him to commandeer his plane, Calder quickly opened the throttles of his Lancaster and took off leaving behind a very angry CO!

When he dropped his Grand Slam on reaching the target it hit the ground around 30 feet from the target and created a crater over 100 feet deep. After release from the Avro Lancaster B.Mk 1 (Special) bomber, the Grand Slam reached near supersonic speed, approaching 715 mph (1150 km/h). When it reached the ground, it penetrated deep underground before detonating. The resulting explosion caused the formation of a cavern of sufficient size to shift the ground around the viaduct’s foundations. With the aid of the Tallboy bombs a massive section of the structure collapsed and it remained closed for the rest of the war. Many other successful operations followed as the Allies closed in on Germany to force their surrender.

After the end of Second World War the Grand Slam crater was filled in but a Tallboy crater remains as a pond a few yards from the Ministry of Home Security target – many other craters can still be found across the area if you look closely. In 1948 the security fence was removed and the Ministry of Supply confirmed to the Verderers that the area had been cleared of explosives. Targets were demolished with the exception of the Ministry of Home Security target which in view of its construction, proved impossible to dismantle. In the circumstances, the surrounding soil was bulldozed over it to cover it up and it appears on the OS map today as a tumulus but if you stand on top of it, some parts of the concrete structure are now clearly visible with the passage of time. The foundations of some other targets also remain visible but the most prominent reminder of the area’s former use are the chalk lines and target markers. Chalk is alien to the acid heath and as a result none of the bordering vegetation will encroach and grow on it. These few reminders apart, the area has returned to nature and is now one of the most tranquil parts of the Forest.

The aerial photograph below was taken on 27 April 1947 and shows Ashley Walk Bombing Range with numerous bomb craters which had not been filled in at that stage – the rectangular construction near the middle is the “sub pens”.

On the Google map below, many features of theAshley Walk Bombing Range can still be seen. The continuous blue line shows the original boundary – click on the markers and red/blue lines for further information.

Unearthed: Secrets of the devastation caused by Grand Slam, the largest WWII bomb ever tested in the UK

The final secrets of Britain's largest-ever conventional weapon of war are being 'unearthed' by archaeologists.

Geophysics experts are using ground-penetrating radar and other high tech methods to 'x-ray' the ground, in a remote area of the New Forest in Hampshire, to shed new light on the most powerful top secret World War Two weapon test ever carried out in the UK.

The weapon - a bomb designed by the British aircraft and munitions inventor, Barnes Wallis, and codenamed 'Grand Slam' - was almost 26 foot long and weighed 22,000 pounds, substantially bigger than any other wartime explosive device ever developed by Britain.

The New Forest test is historically important because it heralded an expansion in the crucial strategic air offensive against key infrastructure targets in Nazi Germany. The first RAF bomber command Grand Slam sortie got underway within hours of the successful test of the bomb.

Four geophysical techniques - ground penetrating radar, magnetometry, electrical resistivity and electrical resistivity tomography - are being used by the archaeologists to assess the damage done to the large concrete target building which has lain buried under a vast mound of earth for the past 66 years.

Barnes Wallis' Grand Slam bomb was designed to seriously damage and destroy buildings, bridges, viaducts and other structures without necessarily having to achieve a direct hit against them. It worked by creating a severe yet localized artificial earthquake.

The one and only test of the bomb took place on 13 March 1945. The weapon was released from a specially adapted Lancaster bomber flying at 16,000 feet over the River Avon just east of the Hampshire town of Fordingbridge, almost two miles west of the New Forest target building. Half a minute after release, the bomb, with its specially designed aero-dynamic fins, hit the target area at more than 700 miles per hour.

Penetrating deep into the ground it produced, after a predetermined nine second interval, a massive explosion which generated the desired artificial earthquake - and created a 70 foot deep 130 foot diameter crater. It was the biggest bomb ever dropped on Britain before or since.

The geophysical investigation and the research operation in the National Archives are expected to reveal just how much damage the earthquake effect had on the target building - but oral history research recently carried out by the New Forest archaeological team suggests that the entire structure was seen to physically move when the bomb exploded some 250 feet away.

After the New Forest test, Grand Slam bombs were used between 14 March and 19 April, 1945 against nine strategically important German targets including the Schildesche railway viaduct near Bielefeld, the Arnsberg railway viaduct, the Nienburg railway bridge, submarine pens near Bremen and German gun batteries on the island of Heligoland.

The Grand Slam campaign played a key role in helping to speed up the defeat of German forces in the final two and half months of the war. Almost 100 Grand Slam bombs were produced of which 42 were used in nine major Bomber Command sorties. Today only five publicly accessible examples survive - in the RAF Museum in north-west London, Brooklands Museum in Surrey, Dumfries and Galloway Aviation Museum, the Battle of Britain Memorial Flight Visitor Centre at RAF Coningsby in Lincolnshire and Kelham Island Museum, Sheffield.

The New Forest National Park Authority's current geophysical survey and historical investigation into Grand Slam is part of a wider project researching and surveying the park's often unappreciated wartime role. Quite apart from Grand Slam, the New Forest was used as a test site for the first Barnes Wallis bouncing bombs, the development of the 'Tallboy' predecessor of Grand Slam, as well as early demonstrations of the Churchill tank. The forest was also home to nine wartime airfields, many of which played a key role in D-Day.

The vast concrete bunker which formed the centre of the Grand Slam target area had originally been built in 1941.

Up till now, historians had thought that it was constructed as a replica enemy submarine pen complex - so as to develop bomb strategy against such targets along occupied Europe's coastline.

However, a series of once-secret documents found in the National Archives by the New Forest National Park research team over the past year have now revealed that the building was originally constructed as a test structure to help develop more effective public air raid shelters.

It appears to have been experimentally constructed out of successive layers of different types of concrete - designed to inhibit the transmission of shock-waves through its walls and roof.

The researchers have even found a previously unknown plan of the building, showing the points at which test detonations were carried out on its roof to assess the effectiveness of the newly developed experimental multi-layer air raid shelter technology.

Bizarrely, Barnes Wallis had actually designed Grand Slam back in 1940 - but political disinterest, bureaucratic obstacles and weapon delivery problems conspired to prevent its final development until early 1945.

"Our geophysical and historical research is helping us to more fully understand and appreciate the testing of Grand Slam - and the New Forest's more general major, yet little known, role in World War Two," said James Brown, an archaeologist at the New Forest National Park Authority.

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It tunnelled deep into the ground at a speed of 700mph before detonating, setting off tremors which were the equivalent of an earthquake.

The crater left at the New Forest test site was 70ft deep and 130ft across, and eyewitness reports suggested that the test building could be seen shaking.

The concrete structure was originally thought to have been an imitation of a German submarine pen, but new evidence suggests that it was in fact an attempt to develop a more robust air-raid shelter, built over five and a half months at a cost of £250,000 (the equivalent of more than £10million today).

Test: When the bomb was dropped on a site in the New Forest, it made a crater 70ft deep and 130ft across

Devastation: The site at a submarine base in Farge, Germany which was hit by a Grand Slam in March 1945

After the end of the war, the site - known as Ashley Range - was returned to its natural state, and the concrete bunker was encased in a mound of dirt because it could not be demolished.

'The military had a responsibility to return it as found,' New Forest archaeologist James Brown told MailOnline. 'But there's a lot of concrete and other structures just left out there.'

Visitors to the forest can still see huge craters, an observation shelter and chalk markings made on the ground in order to help bombers find their targets.

Now researchers from the New Forest National Park Authority hope to use modern scientific techniques to map the devastation caused by the Grand Slam in greater detail.

They will deploy ground-penetrating radar, electrical resistivity tomography and magnetometry to work out to what extent the bunker was damaged by the bomb.

Archaeologists are banned from digging near the site, because of the area's status as part of a national park and its use as a commons for the grazing of ponies and cattle.

Site: An observation shelter situated at the New Forest bombing range where the Grand Slam was tested, which is now being investigated by archaeologists

Despite its image as a peaceful, bucolic patch of England, the New Forest was actually central to the war effort as one of the most active test sites in the country.

As well as the Grand Slam, tanks and bouncing bombs were first tried out in the forest, while the area also hosted nine air fields.

Researchers hope that their hi-tech tools will enable them to reconstruct the history of the site in greater detail than ever before.

Mr Brown said the new research could help the public learn more about the role played by the forest in the war.

'We can create 3D models of all that data that we can have people interact with,' he said.

'Some of our most recent history is some of our rarest - people are focussed on Bronze Age and Roman history and ignore the Second World War.

'It's only recently that interest in Second World War history and archaeology has picked up.'


The Grand Slam bomb, also known as 'Ten Ton Tess', was the largest conventional weapon ever to be developed by the British military.

It was designed by Barnes Wallis, inventor of the bouncing bomb used by the Dambusters, as a way of destroying key sites without having to hit them directly.

He came up with the idea at the beginning of the Second World War, but it was not until towards the end of the conflict that it finally attracted support from top brass and went into production.

The bomb was dropped from a Lancaster bomber and hit the ground at speeds of up to 700mph, tunnelling as deep as 40m into the earth.

Success: Germany surrendered soon after the introduction of the Grand Slam, which obliterated the Valentin submarine pens

It then detonated inside the ground after a nine-second delay, setting off huge vibrations which imitated the effect of an earthquake.

This meant that structures could be damaged or even destroyed by the bomb as long as it fell within a few hundred metres.

The Grand Slam only had to be tested once, in the New Forest in March 1945 - the effect was so extreme that RAF chiefs instantly knew it was ready to be used in the air campaign against Germany.

The next day, one of the bombs was dropped on a railway viaduct in Bielefeld, causing around 100m to collapse in a bid to interrupt German transport and communications.

Aerial: A photograph of the moment when the Grand Slam hit a railway viaduct in Germany the day after being tested in the New Forest

In total, 42 Grand Slams were deployed on nine different sites, including train bridges, gun batteries and structures housing U-boat submarines.

The use of the bomb contributed to the aerial assault on Germany which convinced senior Nazis that the war had finally been lost, leading to the final surrender in May 1945.

After the end of the Second World War, there were still 57 Grand Slams left, but they would never be used in combat again.

Only five complete bombs still survive - they are on display at the RAF Museum, Brooklands Museum, RAF Lossiemouth, RAF Coningsby and the Dumfries and Galloway Aviation Museum.

The Tallboy

The following year, the RAF unveiled its 12,000-lb. Tallboy bomb. The weapons, of which more than 300 were manufactured, were used in nearly three-dozen raids on fortified targets throughout Nazi-occupied Europe including V-1 and V-2 launch sites, railroad tunnels and U-boat pens. The most famous Tallboy target was the German battleship Tirpitz. It was damaged and later destroyed by Lancasters armed with the enormous weapons.

19 March 1945

Pilot Officer P. Martin’s Avro Lancaster B Mk.I Special, PB996, YZ-C, releases the 22,000-pound Grand Slam earth-penetrating bomb over the railway viaduct at Arnsberg, Germany, 19 March 1945. © IWM (CH 15735) The Grand Slam bomb drops away from the No. 617 Squadron Lancaster B Mk.I Special, YZ-C, 19 March 1945. © IWM (CH 15374)

19 March 1945: Modified Avro Lancaster B Mk.I Special heavy bombers of No. 617 Squadron, Royal Air Force, attacked the railway viaduct at Arnsberg, Germany, using the 22,000 pound (9,979 kilogram) Grand Slam earth-penetrating bomb. The bomb had been first used just days before, 14 March, against another railway viaduct.

The Grand Slam was the largest and heaviest aerial bomb used during World War II. It was designed by aircraft engineer Barnes Neville Wallis, and was scaled up from his earlier, smaller “Tallboy.” (Wallis also designed the “Upkeep” Special Mine used to attack hydroelectric dams in the Ruhr Valley in 1943.)

The Grand Slam bomb dropped by Flying Officer Martin’s Avro Lancaster explodes underneath the railway viaduct at Arnsberg, Germany. Bomb craters from previous unsuccessful attacks are visible in this RAF photograph. © IWM (CH 15378)

Wallis’ idea was that a very heavy, supersonic bomb could penetrate deep into the earth and detonate, causing an “earthquake” which could destroy nearby heavily protected targets.

Tall Boy and Grand Slam Deep Penetration Bombs (British Explosive Ordnance, Part 1, Chapter 7)

The Grand Slam bomb (officially, “Bomb, D.P. , 22,000-lb., Mk I”) was 25 feet, 5 inches (7.747 meters) long and had a maximum diameter of 3 feet, 10 inches (1.168 meters). When fully loaded with the explosive material, Torpex, the bomb weighed 22,400 pounds (10,160 kilograms).

Completed bomb casings for Wallis’ smaller 12,000-pound “Tallboy” deep penetration bomb. The individual weight is stenciled on each casing. (Tyne & Wear Archives)

The bomb case was cast of steel at the Clyde Alloy and Steel Company, Glasgow, Scotland, then, after several days of cooling, machined to its precise shape. The casing made up approximately 60% of the bomb’s total weight. At the nose, the casing had a wall thickness of 7.75 inches (19.685 centimeters).

A “Bomb, Deep Penetration, 22,000 Pounds”—the Grand Slam—lifted by a crane at a Royal Air Force bomb dump. © IWM (CH 15369)

The bomb case was filled with approximately 9,200 pounds (4,173 kilograms) of molten Torpex, with a 1 inch (2.54 centimeters) topping of TNT. Torpex was an explosive designed for torpedo warheads and depth charges. It was made up of approximately equal quantities of two other explosives, Research Department Formula X (RDX), 42%, and trinitrotoluol (TNT), 40%, mixed with 18% powdered aluminum and wax. The resulting combination was approximately 1.4 times more powerful than TNT alone. About one month was required for the explosive to cool after being poured into the bomb case.

Because of its size and weight, the only Allied bomber capable of carrying the Grand Slam was a specially modified Avro Lancaster B.I Special, flown by No. 617 Squadron, Royal Air Force, “The Dambusters.”

Wallis intended for the Grand Slam to be dropped from very high altitudes so that during its fall, it would go supersonic. The bomb had large fins that were offset 5° to the right of the centerline to cause it to rotate for stability. However, the bombers could not carry it to the planned release altitude, and it was typically dropped from approximately 9,000 feet (2,743 meters). Its very sleek design did allow it to come close to the speed of sound, however, and its stability made it a very accurate weapon. The bomb was capable of penetrating 20-foot-thick (6 meters) reinforced concrete roofs of submarine bases. ¹

Arnsberg railway viaduct following Grand Slam bombing attack.

Barnes Neville Wallis, Esq., M. Inst. C.E., F.R.Ae.S., Assistant Chief Designer Vickers-Armstrongs Ltd., was appointed Commander of the Most Excellent Order of the British Empire (Civil Division), by His Majesty, King George VI, 2 June 1943.

Sir Barnes Neville Wallis C.B.E., was knighted by Her Majesty, Queen Elizabeth II, 13 December 1968.

Sir Barnes Neville Wallis C.B.E.

Question about Tallboy/Grand Slam bombs

I think that Tallboy, dropped from as high as a Lancaster could carry it would just go supersonic. Grand Slam maybe a bit faster. Certainly not 3700 fps.

After an excellent landing you can use the airplane again.

I seem to recall a statement by Eric Brown in one of his books that when they were doing high speed research with Spitfires i.e. vertical dives, they would reach a point where throttling back the engine had no effect because all the speed was being provided by the aircraft mass - and they were hitting 500 mph with a lot more drag and a lot less mass than a Tallboy!

Also I think it was Sir Stanley Hooker who once did a back of a fag packet calculation that a Spitfire flat out in level flight was producing about 1000 lb of thrust. Sabres got close to the sound barrier in level flight with about 5000 lb thrust.

So a well streamlined bomb with 12000 lb (or 22 000 lb) of gravitational thrust? Through the sound barrier easy.

Grand Slam Bomb - History

It’s called the GBU-43/B Massive Ordnance Air Blast, nicknamed the Mother of All Bombs, and it is the largest non-nuclear bomb currently in the U.S. Air Force’s arsenal. For years, America’s MOABs have lain dormant: the high potential for collateral had kept the weapon out of action, with smaller and more precise JDAMs and Hellfire missiles preferred against insurgent forces that intermeshed with civilian populations. On April 13, 2017, the USAF broke this trend by dropping one of these massive weapons on top of ISIS positions in Afghanistan. But just how powerful is the GBU-43/B? The bomb weighs 22,600 lbs, filled with 18,700 lbs of explosives. The MOAB blast radius is 1 mile and yield is equivalent to 11 tons, or 22,000 lbs, of TNT.

For a sense of scale, let’s compare the MOAB to the most destructive single weapon systems of the Second World War.

Grand Slam: The Allies’ MOAB

The Grand Slam bombs were the largest conventional bombs of the war. The 22,000 lb bomb carried 9,000 lbs of explosives with a 13,000 lb yield. Delivered by modified Lancaster bombers, the Grand Slam, along with the smaller Tall Boy of similar design, was a deep penetration bomb intended for use against hardened structures such as railway bridges and submarine pens. By the end of the war the Allies would drop 41 of these bombs dropped on targets in Germany, mainly bridges and viaducts.

Compared with the MOAB, the Grand Slam of course still falls short, with a yield of less than 60% of the MOAB’s.

How Many B-29s Would It Take to Match a MOAB?

The B-29 boasted perhaps the largest standard bomber payload of the war. When armed with 40 AN-M64 500 lb bombs, the B-29 had a devastating 20,000 lb payload. When loaded with 267 lbs of TNT, the 40 AN-M64’s made for a total TNT weight of 10,680 lbs. As such, it would take two fully loaded B-29 Superfortresses equipped with 80 AN-M64 bombs to match the firepower of one MOAB.

B-29 bombers flying a daylight mission to Japan.

How About Germany’s Heavy Bombers?

Germany’s bombers would not even come close to the destructive power of a MOAB. These were far lighter than their Allied counterparts, owing to Germany’s blitzkrieg doctrine emphasizing light and medium bombers to provide coordinated support for fast-moving tanks and mechanized infantry.

The only German purpose-built strategic bomber of the war to see significant wartime use was the He-177 Ural bomber. When equipped with six 2,209 lb SC1000 bombs, the He-177 could carry a maximum payload of over 13,000 lbs. With L2 bombs, the SC1000 variant with the most efficient weight to charge ratio, the Ural bomber could carry 7800 lbs of explosives. Thus, to match the firepower of one MOAB, it would require three of Hitler’s heaviest bombers loaded to their maximum payload.

Hitler’s Wunderwaffe vs the MOAB

Compared to the MOAB, Hitler’s Wunderwaffe were even more outgunned than his Luftwaffe.

The V2 rocket had a 2,150 lb warhead filled with 2,010 lbs of explosive amatol 60/40, an amazing 93% weight to charge ratio, but far short of the MOAB yield. It would take 11 V2 rockets to equal the destructive power of one MOAB.

An American soldier inspects the engine of a V-2 pilotless rocket bomb on the assembly line at the underground factory near Nordhausen.

The massive 800mm Schwerer Gustav railway gun, with high explosive shells weighing up to 10,600 lbs, only had an explosive weight of 1,500 lbs, meaning that the mighty Gustav would have to lob nearly 15 shells in order to match the destructive capabilities of one MOAB. This would be approximately equivalent to the average daily rate of fire for the Gustav of about 14 shells a day during the siege of Sevastopol.

No Match For the A-Bomb

If the MOAB had been in World War II, it would have reigned supreme as the most powerful single weapon system of the war. That is, up until 8:12 a.m. on August 6, 1945. On that day, the world was formally introduced to a scale of destruction never before created by man. The Little Boy uranium bomb produced a blast estimated to be between 13,000-20,000 TONS of TNT. The plutonium bomb Fat Man at 20,000-22,000 tons of TNT would further outpace the scale of destruction caused by any single weapon system in the history of man-kind.

Compared to these giants, the MOAB is less than one-thousandth the blast radius. However, looking back at how the MOAB compares to the weapons of WWII helps put the sheer power of the bomb into perspective.

Watch the video: WWII Tallboy bomb explodes during effort to defuse it in Poland


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