Daily Archives: March 19, 2019

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 teh railway viaduct at Arnsberg, Germany, 19 March 1945. (Imperial War Museum)
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. (Imperial War Museum)
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 exploeds underneath the railway viaduct at Arnsberg, Germany. (Imperial War Museum)
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, Medium Capacity, 22,000 Pounds, lifted by a crane at a Royal Air Force bomb dump. (Imperial War Museum)
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.

¹ “The striking velocity of the bomb, when released at an altitude of 16,000 ft. and an air speed of 200 m.p.h., is stated at 1,097 ft./sec., at which speed is has developed a rotational velocity of 60 r.p.m.” —British Explosive Ordnance, Part 1, Chapter 7

© 2019, Bryan R. Swopes

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19 March 1937

Amelia Earhart's Lockheed Electra 10E Special, NR16020, in a hangar at Wheeler Field, Honolulu, Territory of Hawaii, 19 March 1937. (Hawaii's Aviation History, http://hawaii.gov/hawaiiaviation )
Amelia Earhart’s Lockheed Electra 10E Special, NR16020, in a hangar at Wheeler Field, Honolulu, Territory of Hawaii, 19 March 1937. (Hawaii’s Aviation History)

19 March 1937: After her 15 hour, 47 minute, overnight flight from Oakland, California, Amelia Earhart’s Lockheed Electra 10E Special NR16020 was placed in a hangar at Wheeler Army Airfield, Honolulu, for maintenance and repair. During the flight, a propeller pitch change mechanism had failed. Inspection revealed that both propeller hubs were badly galled “due to improper or insufficient lubrication.” They were overhauled by the Army Air Corps’ Hawaiian Air Depot at Luke Field, then re-installed on the Electra.

At 11:15 a.m. on the 19th, Paul Mantz and two friends took the Electra for a test flight, then repositioned to Luke Field on Ford Island, with its longer, hard-surfaced runway, for an early morning takeoff on the second leg of the around-the-world flight.

Amelia Earhart's Lockheed Electra 10E Special, NR16020, with engines running at Wheeler Field, prior to repositioning to Luke Field, 19 March 1937. (Hawaii’s Aviation History, http://hawaii.gov/hawaiiaviation )
Amelia Earhart’s Lockheed Electra 10E Special, NR16020, with engines running at Wheeler Field, prior to repositioning to Luke Field, 19 March 1937. (Hawaii’s Aviation History)

© 2019, Bryan R. Swopes

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