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.)
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.
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).
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).
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
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.
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
12 November 1944: No. 9 Squadron and No. 617 Squadron (Dambusters), Royal Air Force, sent a force of 32 Avro Lancaster long range heavy bombers to attack the 49,948 metric-ton-displacement Kriegsmarine battleship KMS Tirpitz at Tromsø Fjord, Norway. The attack was filmed by a photo aircraft of No. 463 Squadron, Royal Australian Air Force.
The Lancasters were armed with 12,030 pound (5,457 kilogram) Tallboy bombs. They bombed from altitudes from 12,000 to 16,000 feet (3,658–4,877 meters). Two of the bombs hit the battleship, one was a very near miss and another three also were close enough that they probably contributed to the overall damage. Many other Tallboys landed within the torpedo nets that surrounded the ship and cratered the seabed, removing the sandy bottom which had been built up under Tirpitz‘ hull to prevent her from sinking. Tirpitz immediately began to list and was then rocked by an internal explosion. It capsized and sank to the sea bed. As many as 1,204 sailors were killed.
Tirpitz was a Bismarck-class battleship armed with a main battery of eight 38-centimeter (15-inch/52-caliber) guns in four turrets. These guns had a maximum range of 22.7 miles (36.5 kilometers) when firing a 1,800 pound (816 kilogram) projectile. The German Navy did not use its heavy warships to directly engage the British fleet, but instead to raid the Atlantic convoys. The merchant ships with their destroyer escorts were defenseless against a battleship or battle cruiser. Allied forces expended tremendous effort and resources to contain or destroy Tirpitz throughout the war.
The Avro Lancaster was a four-engine long range heavy bomber. It wasn’t as fast as the American B-17 Flying Fortress, but was capable of flying longer distances with a heavier bomb load. It was operated by a crew of seven: Pilot, flight engineer, navigator, radio operator, bomb aimer/nose gunner, top gunner and tail gunner. The “Lanc” was 69 feet, 4 inches (21.133 meters) long, with a wingspan of 102 feet (31.090 meters) and had an overall height of 20 feet, 6 inches (6.248 meters). It had a maximum takeoff weight (MTOW) of 72,000 pounds (32,657 kilograms) when carrying a 22,000 pound (9,979 kilogram) Grand Slam bomb.
The Lancaster was powered by four liquid-cooled, supercharged, 1,648.96-cubic-inch-displacement (27.01 liter), Rolls Royce Merlin XX or Packard V-1650 single overhead camshaft (SOHC) 60° V-12 engines, which were rated at 1,480 horsepower at 3,000 r.p.m. to 6,000 feet (1,829 meters). They turned three-bladed de Havilland Hydromatic constant-speed propellers which had a diameter of 13 feet (3.962 meters) through a 0.420:1 gear reduction.
These Merlin engines, the same as those powering Supermarine Spitfire, Hawker Hurricane and North American P-51 Mustang fighters, gave the Lancaster a maximum speed of 282 miles per hour (456 kilometers per hour) at 13,000 feet (3,962 meters) at a weight of 63,000 pounds (28,576 kilometers per hour). The service ceiling was 21,400 feet (6,523 meters) and maximum range was 2,530 miles (4,073 kilometers).
Defensive armament for a standard Lancaster consisted of eight Browning Mark II .303-caliber machine guns in three power turrets, nose, dorsal and tail. Modified bombers deleted various combinations of guns to reduce weight.
The Tallboy (Bomb, Medium Capacity, 12,000 lb) was a special demolition bomb designed to be dropped from high altitude, reach supersonic speeds, then penetrate as far as 90 feet (27 meters) into the ground before detonating. It was built of a specially hardened steel casing filled with 5,200 pounds (2,358 kilograms) of Torpex explosive. The bomb was designed by Barnes Wallis, who had also designed the special bomb used by the Dambusters in their famous 1943 attack on the Ruhr Valley hydroelectric dams, as well as the Grand Slam, a 22,000-pound (10,000 kilogram) scaled-up version of the Tallboy. The Tallboy and Grand Slam bombs were very successfully used against U-boat pens and heavily fortified underground rocket facilities.
22 July 1943: A Royal Air Force official photographer visited No. 617 Squadron, The Dambusters, at their base at RAF Scampton, Lincolnshire, England. These photographic images are part of the Ministry of Information Second World War Colour Transparency Collection.
Wing Commander Guy Penrose Gibson, D.S.O. and Bar, D.F.C. and Bar, was awarded the Victoria Cross by His Majesty King George VI in a ceremony at RAF Scampton, Lincolnshire, England. Wing Commander Gibson received the medal for his leadership of No. 617 Squadron, The Dambusters, during Operation Chastise, an attack on Germany’s Ruhr Valley hydroelectric dams, 16–17 May 1943.
The Victoria Cross ranks with the George Cross as the United Kingdom’s highest award for gallantry.
The first British medal to be created for bravery, the Victoria Cross was instituted in 1856, with the first recipients being personnel honored for their gallantry during the Crimean War.
The bronze cross pattée, which bears the inscription “FOR VALOUR,” is cast from the metal of Russian guns captured at Sevastopol during the Crimean campaign. The Victoria Cross is awarded “for most conspicuous bravery, or some daring or pre-eminent act of valour or self-sacrifice, or extreme devotion to duty in the presence of the enemy.”
Air Ministry, 28th May, 1943.
ROYAL AIR FORCE.
The KING has been graciously pleased to confer the VICTORIA CROSS on the undermentioned officer in recognition of most conspicuous bravery: —
Acting Wing Commander Guy Penrose GIBSON, D.S.O., D.F.C. (39438), Reserve of Air Force Officers, No. 617 Squadron: —
This officer served as a night bomber pilot at the beginning of the war and quickly established a reputation as an outstanding operational pilot. In addition to taking the fullest possible share in all normal operations, he made single-handed attacks during his “rest” nights on such highly defended objectives as the German battleship Tirpitz, then completing in Wilhelmshaven.
When his tour of operational duty was concluded, he asked for a further operational posting and went to a night-fighter unit instead of being posted for instructional duties. In the course of his second operational tour, he destroyed at least three enemy bombers and contributed much to the raising and development of new night-fighter formations.
After a short period in a training unit, he again volunteered for operational duties and returned to night bombers. Both as an operational pilot and as leader of his squadron, he achieved outstandingly successful results and his personal courage knew no bounds. Berlin, Cologne, Danzig, Gdynia, Genoa, Le Creusot, Milan, Nuremberg and Stuttgart were among the targets he attacked by day and by night.
On the conclusion of his third operational tour, Wing Commander Gibson pressed strongly to be allowed to remain on operations and he was selected to command a squadron then forming for special tasks. Under his inspiring leadership, this squadron has now executed one of the most devastating attacks of the war—the breaching of the Moehne and Eder dams.
The task was fraught with danger and difficulty. Wing Commander Gibson personally made the initial attack on the Moehne dam. Descending to within a few feet of the water and taking the full brunt of the antiaircraft defences, he delivered his attack with great accuracy. Afterwards he circled very low for 30 minutes, drawing the enemy fire on himself in order to leave as free a run as possible to the following aircraft which were attacking the dam in turn.
Wing Commander Gibson then led the remainder of his force to the Eder dam where, with complete disregard for his own safety, he repeated his tactics and once more drew on himself the enemy fire so that the attack could be successfully developed.
Wing Commander Gibson has completed over 170 sorties, involving more than 600 hours operational flying. Throughout his operational career, prolonged exceptionally at his own request, he has shown leadership, determination and valour of the highest order.
—The London Gazette, Tuesday, 25 May 1943, No. 3630 at Page 2361
16–17 May 1943: Nineteen modified Avro Lancaster B.III Special long-range heavy bombers of No. 617 Squadron, Royal Air Force, carried out Operation Chastise, a low-level night attack against four hydroelectric dams in the Ruhr Valley.
The purpose of the attack was to disrupt German steel production. It was estimated that 8 tons of water were required to produce 1 ton of steel. Breaching the dams would reduce the available water and hydroelectric power, disrupt transportation of materials on the rivers, and flood iron ore and coal mines and power plants. If the dams were destroyed, it was believed that the effects would be the same as attacks against 26 categories of industrial targets further down the Ruhr Valley.
Led by 24-year-old Wing Commander Guy Penrose Gibson, D.S.O. and Bar, D.F.C. and Bar, a veteran of 172 combat missions, the aircrews of No. 617 Squadron dropped a spinning cylindrical bomb, code-named “Upkeep,” from a height of just 60 feet (18.3 meters) over the reservoirs behind the dams, while flying at precisely 240 miles per hour (386.2 kilometers per hour).
The 9,250-pound (4,195.8 kilogram) Vickers Type 464 bomb was designed to skip along the surface and to strike the dam, and then sink to the bottom. There, a pressure detonator exploded the 6,600 pound (2,994 kilogram) Torpex charge directly against the wall with the water pressure directing the energy through the wall.
Nineteen Lancasters took off from RAF Scampton in Lincolnshire, England, beginning at 9:28 p.m. on the 16th, and flew across the North Sea at only 100 feet (30.5 meters) to avoid being detected by enemy radar. The bombers succeeded in destroying the Möhne and Eder dams and damaging the Sorpe. A fourth dam, the Ennepe, was attacked but not damaged. The last surviving bomber returned to base at 6:15 a.m. on the 17th.
Of the nineteen Lancasters launched, two were damaged and turned back before reaching the targets. Six were shot down and two more collided with power lines during the low-level night flight. Of 133 airmen participating in the attack, 53 were killed.
For his planning, training and execution of the raid, Wing Commander Gibson was awarded the Victoria Cross by King George VI. An additional 33 survivors were also decorated. 617 Squadron became known as “The Dambusters.” A book, The Dam Busters, was written about the raid by Paul Brickhill, who also wrote The Great Escape. A 1955 movie starred Richard Todd, O.B.E., as Wing Commander Gibson. There have been reports that a new movie is planned.
The Avro Lancaster B.III Special was a four-engine long range heavy bomber modified to carry the Type 464 bomb. It was operated by a crew of seven: Pilot, flight engineer, navigator, radio operator, bomb aimer, nose gunner and tail gunner. The “Lanc” was 69 feet, 6 inches (21.184 meters) long with a wingspan of 102 feet, 0 inches (31.090 meters) and overall height of 20 feet, 4 inches (6.198 meters), in 3-point position. The Lancaster’s wings had a total area of 1,300.0 square feet (120.8 square meters). Their angle of incidence was 4° and the outer wing panels had 7° dihedral. The span of the horizontal stabilizer was 33 feet, 0 inches (10.058 meters). The modified bomber had an empty weight of 35,240 pounds (15,984.6 kilograms and a maximum takeoff weight (MTOW) of 60,000 pounds (27,215.5 kilograms).
The Lancaster B.III Special was powered by the Packard Motor Car Company’s license-built version of the Rolls-Royce Merlin 24, the Packard V-1650-1 Merlin 224. These were liquid-cooled, supercharged, 1,648.96-cubic-inch-displacement (27.022-liter) single overhead cam (SOHC) 60° V-12 engines with four valves per cylinder and a compression ratio of 6.0:1. The Merlin 224 used a two-speed, single-stage supercharger. 100/130-octane aviation gasoline was required. The engine had a Normal Power rating of 1,080 horsepower at 2,650 r.p.m. and 9,500 feet (2,896 meters); Military Power, 1,240 horsepower at 3,000 r.p.m. at 11,000 feet (3,353 meters); and 1,300 horsepower at 3,000 horsepower with 54.3 inches of manifold pressure (1.84 Bar) for Takeoff. The Merlins drove three-bladed de Havilland Hydromatic quick-feathering, constant-speed propellers which had a diameter of 13 feet (3.962 meters). The propeller gear reduction ratio was 0.477:1. The V-1650-1 was 6 feet, 7.7 inches (2.024 meters) long, 2 feet, 6.0 inches (0.762 meters) wide and 3 feet, 6.6 inches (1.082 meters) high. It weighed 1,512 pounds (685.8 kilograms).
These engines gave the Lancaster a cruising speed of 200 miles per hour (321.9 kilometers per hour) and maximum speed of 272 miles per hour (437.7 kilometers per hour). The service ceiling was 24,700 feet (7,528.6 meters) and maximum range was 2,530 miles (4,071.6 kilometers).
Defensive armament for a standard Lancaster consisted of eight air-cooled Browning .303-caliber Mark II machine guns in three power turrets, nose, dorsal and tail. The Lancasters assigned to Operation Chastise had the dorsal turret deleted to reduce weight and aerodynamic drag. The gunner normally operating that turret was moved to the front turret, relieving the bomb aimer to deal with the operation of the specialized mission equipment.
7,377 Avro Lancasters were built. Only two remain in airworthy condition.
Highly Recommended: The Dam Busters, by Paul Brickhill. Evans Brothers, London, 1951