RAF Wing Commander Johnnie Fauquire, CO of N0. 617 Squadron, ran through his preflight checklist on March 14, 1945, in Avro Lancaster YZ-J, while Squadron Leader “Jock” Calder did the same in nearby YZ-S. Though the routine was familiar, the Lancaster B1 Specials that both pilots were readying for takeoff were anything but. To save weight, the front and dorsal turrets had been removed. Also missing were the radio operator and his equipment, armor plating, chemical toilet, fire axes, tools and crew ladder. The navigatior’s seat had even been replaced by a wicker chair.

There was also a striking addition: Suspended beneath both Lancs was a streamlined gray shape more than 25 feet long and nearly 4 feet in diameter, encircled by a massive chain—the first operational 10-ton Grand Slams, the largest and heaviest bombs of World War II. Their target: the massive Bielefeld twin railroad viaduct near Bremen, Germany, a vital link bringing armaments to the Wehrmacht defending the Ruhr Valley.

Both pilots started their engines, Rolls-Royce Merlin 24s, but one of Farquire’s starboard engines quickly seized, prompting the wing commander to sprint to Calder’s aircraft, intent on commandeering his plane. Meanwhile Calder—unwilling to lose his chance to make history—pushed the throttles forward. Leaving his fuming CO behind.

The Grand Slam was a staggering load, even for the Lancaster, WWII’s champion weightlifter. Once Calder’s bomber was in the air, its wings spread in an arc, curving upward at the tips as they took the strain. Observers in other aircraft eyed YZ-S in disbelief, fearing its main spar might fail, causing the wings to fold.

A single Grand Slam brought down seven spans of the Bielefeld railroad viaduct on March 14, 1945. (IWM C 5089)

Calder was well aware that the only way to placate Fauquier would be to bring down the viaduct. The maximum he could coax out of YZ-S was 210 mph and 12,000 feet of altitude en route to Germany. When the viaduct finally came into view, it was surrounded by a moonscape of overlapping craters. Months of raids by the U.S. Eighth Air Force and RAF had caused some damage to the structure, but it had been quickly repaired by the Germans.

At 4:28 P.M., bomb aimer Clifford Crafer pressed the release button and the explosive bolts in the mounting chain fired. The control column kicked in Calder’s hands as the Lanc leaped 500 feet. Looking like a gigantic gray fish, the bomb fell for 35 seconds before spearing into the marshy ground near the viaduct. Then a monstrous mushroom of smoke and mud erupted. When it cleared, the pilot of a camera-equipped de Havilland Mosquito yelled into Calder’s VHF headphones, “You’ve done it!” Seven spans, and more than 460 feet of both viaducts, were gone.

The celebrated “Dambuster” squadron would drop 40 more Grand Slams and several hundred 6-ton Tallboys before war’s end, but Bielfeld was its supreme achievement, validating engineer Barnes Wallis’ efforts to prove his big-bomb theory to a skeptical Air Ministry.

Following the destruction of the Mohne and Eder dams in May 1943, Bomber Command had pondered how to use 617 Squadron, which had been formed specifically for that operation. Air Chief Marshal Arthur Harris decided: “We’ll make them a special duties squadron…whenever the Army or Navy want a dam or a ship or something clouted, we’ll put 617 on it.”

A 22,000-lb "Grand Slam" is moved onto a trolley by crane in the bomb dump at Woodhall Spa, Lincolnshire, for an evening raid on the railway bridge at Nienburg, Germany. (IWM CH 15369)

When Guy Gibson, who had led the dams operation, left on a tour of the U.S., George Holden became 617’s new commanding officer. A veteran of 43 operations with a Distinguished Service Order and two Distinguished Flying Crosses to his credit, Holden had voluntarily dropped in rank from wing commander to squadron leader to join 617.

The first targets chosen were German canals, a heavily defended network of vital conduits carrying everything from coal to preassembled aircraft sections. The squadron initially targeted the Dortmund-Ems canal, still in constant use despite being under attack since 1940. Though the original plan envisioned using the same “bouncing bombs” that had brought down the dams, in the end the Lancasters took off with the new 12,000-pound HC (high capacity) blast bomb. The first attempt, on September 14, was recalled while they were over the North Sea. As David Maltby’s aircraft was turning back, a wingtip hit the sea and the plane cartwheeled in, killing everyone on board.

The following night, on Holden’s 30th Birthday, they tried again. Most of Gibson’s crew from the dams raid were flying with Holden when, as they crossed the German border, flak hit their Lanc’s starboard fuel tank. Streaming flames, the bomber hit the ground and exploded.

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Flight Lt. Mick Martin led the rest as they tried to find the canal in the darkness and fog. Flak downed another Lancaster, and in the murk Les Knight, whose Upkeep bomb had breached the Eder dam in May, flew into the trees, putting out two engines and damaging the rudders. The ever-professional Knight radioed Martin: “I have lost two engines. May I have permission to jettison, Sir?” After receiving Martin’s OK, Knight jettisoned the bomb and fought to keep the crippled Lanc in the air, but finally told his crew, “Jump, and God bless you,” knowing he would be unable to follow. Soon after, his bomber crashed and burned.

Encountering intense flak, Ralph Allenbrook first replied to a call from Martin with: “Hang on until I get out of this,” and later, “returning to base.” Then there was only silence. Flak had torn off one of the Lanc’s wings, and he crashed into the canal. Bill Divall’s plane and crew were also lost. Martin and Dave Shannon briefly managed to sight the canal, but their bombs fell a few feet too far away to breach it.

By the time the survivors landed, two-thirds of the crews—including many men who had participated in the Dambuster raid—were dead. Counting earlier operations and Maltby’s loss, the new CO and 12 crews had died within a couple of weeks. Mick Martin offered to go back the next night, but instead, was promoted to squadron leader. After such appalling losses, the crews were given an extended rest while the brass reevaluated 617’s role.

Britain had entered WWII with a strategic plan to attack military and industrial targets by day based on the same mistaken theory that both Germany and the United States had at first adopted: that unescorted bombers could fend off enemy fighters. After some disastrous missions, the British switched to night operations.

Based on optimistic reports of returning bomber crews, the Air Ministry was initially convinced that Bomber Command was inflicting serious damage on German industry and infrastructure. That illusion was shattered in August 1941 by the Butt Report, an evaluation of 600 bomb-release photographs. Two-thirds of RAF bombers had not even reached their assigned target area, and only one in three of those claiming to have attacked it had actually bombed within five miles of the objective. After another study had reached a similar conclusion, the Air Ministry modified its strategy: “Our primary objective is the progressive destruction and dislocation of the German military, industrial and economic system and undermining the moral of the German people.”

Two years later, the January 1943 Casablanca Conference reiterated the same goal. A directive to Air Chief Marshal Harris and U.S. Army Air Forces Maj. Gen. Ira Eaker advised “undermining the moral of the German people to the point where their capacity for armed resistance is fatally weakened.” Conference leaders ignored clear evidence from the Blitz, when the bombing of British cities and the deaths of 60,000 civilians had only stiffened Britons’ resolve to keep fighting.

Scientist and engineer Barnes Wallis, inventor of the Upkeep bomb, had long sought to change Britain’s bombing strategy. Aware the Germans were protecting sites with up to 20 feet of reenforced concrete, he had been pondering the effects of shock waves on masonry. While London’s Waterloo Bridge was being built, he recalled, the tops of the concrete piles being driven into the bed of the Thames River had kept shattering. He learned from a 1935 article in the journal of the Institute of Engineers that drop-hammers had sent shock waves down the piles; at the bottom they bounced back up off the clay riverbed at more than 1,000 mph.Since concrete is strong in compression but weak in tension, the tops of the piles had exploded off.

To get the same effect on a concrete masonry structure, Wallis postulated, a 6- or even a 10-ton bomb with a thick, hard steel casing should be aimed for a near miss instead of a direct hit. When the bomb exploded underground, the supersonic shock wave it generated would severely damage or destroy the structure. Even if the Germans increased the roof thickness, it would be no defense against an “earthquake bomb” which could also create a huge subterranean cavern. The structure might fall into the void or have its foundations fatally undermined. When such a bomb was used on a bridge or viaduct, if the shock wave didn’t destroy it, the cavern would take its supports away and swallow it.

When Wallis published his first paper on his earthquake bomb theory in May 1940, it was met with lukewarm interest or derision by officials. At the time, Britain was expecting an invasion, and every industry head was already fully engaged in vital war projects. No aircraft capable of carrying a 6-tonbomb was available, and even so, area bombing philosophy dictated that a stick of 12 1,000-pound bombs made more sense than one 12.000-pound weapon. Turning Wallis’ theory into practice would have to wait.

By late 1943, the RAF was operating more than 1,000 four-engined heavy bombers, and technology and tactics had advanced dramatically. Radar had revolutionized night navigation. Pathfinders were marking targets with cascades of flares and colored incendiaries. Circling master bombers warned crews of dummy targets and bogus markers, or when bombs were drifting off target. The new Mark XIV computing sight and GH, a blind-bombing system, enabled RAF crews to drop a new generation of bombs accurately at night, even through cloud cover. Allied air forces were laying waste to vast areas, including enemy cities, factories, and industrial regions. But the effects on munitions production and moral were marginal. Germany had begun decentralizing manufacturing in 1940. From late 1943 until war’s end, German armament and aircraft production increased three-fold, tanks six-fold.

In mid-1943, Sir Wilfred Freeman, Ministry of Aircraft Production chief, sent for Wallis and asked: “Remember that crazy idea of yours back in 1940 about big bombs, a 10-tonner and a 6-tonner? You wrote a paper about it—to penetrate deep into the earth and cause an earthquake.” Wallis responded, “Ah yes, I seem to have had a lot of crazy ideas then.” Freeman then asked, “How soon can you let me have some?” Only two foundries in the country were capable of casting and hardening the special steel to enable the bombs to plough deep into solid earth, and both facilities were already involved in vital war work. ”About four or five months,” Wallis replied, “if I can get the facilities.”

No 617 Squadron's CO Leonard Cheshire (far right) along with Mosquito pilots, Charles Pickard and William Blessing wait for a ceremony at Buckingham Palace on, July 28, 1943. Of the three, only Cheshire would survive the war. (IWM CH 1706)

Meanwhile, 617 Squadron had a new commanding office, Leonard Cheshire, who would play a key role in validating the 6-ton Tallboy bomb’s effectiveness. On his third 30-mission tour when few lived to complete one, Cheshire had already nursed several badly damaged bombers back home, and held two DSOs and the DFC. At 27, Cheshire became the RAF’s youngest group Captain.

On taking command, he learned the name of everyone on the base, inspiring such loyality that his men started calling themselves “The Cheshire Cats.” Ordered to cross the enemy coast at 2,000 feet (armchair strategists that held this was too high for light flak and too low for heavy, but Cheshire knew that it was ideal for medium Flak), he refused: They would cross at either 200 feet or 20,000. After several raids where low clouds and smoke resulted in poor results, Cheshire was allowed to dispense with Pathfinder assistance and do the job himself at low level. He would develop the most precise target marking of the war.

The first operations using his technique were against V-1 flying- bomb sites in the Pas de Calais, where he dived to 5,000 feet to place markers on targets. On February 8, 1944, Cheshire flew his Lancaster over the Gnome-Rhone factory near Limoges three times to warn French workers of an impending attack. Then dropped flares squarely on the roof at 50 feet—after which the bombers wrecked the plant. Cheshire repeated that performance on March 1 at the BMW factory at Albert, shutting down production, and the needle-bearing plant at St. Etinne, destroying 80 percent of the factory. Next 617 flattened the Michelin tire works at Clearmont Ferrand, ending the supply of 24,000 tires a month to the Nazis. Using pinpoint marking, 617 also wrecked the marshalling yards at Munich and Brunswick. Cheshire considered Munich his most successful raid of the war: More than 90 percent of the bombs hit the target, causing more damage in a single raid than the total of many earlier ones by the RAF and USAAF

Wing Commander Cheshire marks the Gnome-Rhone aero-engine factory at Limoges, France, for destruction. His low level technique placed the incendary bombs squarly on the target. (IWM HU 93014)

Knowing he’d be lucky to survive marking targets in a four-engined bomber, Cheshire asked whether the Americans could spare one of their P-51s, and a few days later a Mustang arrived. Although he hadn’t flown a single-engine plane since his training days, his first flight came in a raid. From then on, marked by Cheshire in his Mustang, targets in Germany, Italy and occupied France burned, one after another.

One night Cheshire and his deputy, squadron leader Les Monroe, saw a truck heading toward the bomb dump, carrying tarpaulin-covered objects that the driver had been told were new boilers for the cookhouse. “You’re going the wrong way,” said Cheshire. “Let’s have a look at these, Les.” When they pulled back the cover and saw two long, streamlined monsters with sharp noses, an awed Monroe said, “Wallis’ Tallboys.” The armament officer later apologized; the bombs had been arriving for a week, but he had been told to keep quiet about them.

On June 8, Cheshire led 19 Lancasters carrying Tallboys and equipped with. The new SABS bombsight (similar to the American Norden). Their target: the railway tunnel at Samur, France. Believing the main D-Day landing would come in the pas de Calais area, Germany’s high command had kept most of its armored divisions in the North. When they realized Normandy was the real thing, the Germans began trying to move on them—efforts the Lancs meant to impede.

Two Grand Slams collapsed the roof of the sumbarine pens at Farge, Germany. (IWM CH 9136)

Photos taken the next day showed what the Tallboys could do. Craters around the tunnel mouth averaged 84 feet in diameter and 30 feet deep. One of the bombs had blown out the hill and exposed the tunnel itself, filled with rubble. The Germans worked for six weeks to reopen the tunnel—just in time for the Allies to use it.

After D-Day, German E-boats, operating from the pens in Le Harve and Boulogne with roofs of reenforced concrete 16 feet thick, attacked convoys ferrying men and equipment to Normandy. Though the Tallboys hadn’t been designed for direct hits on concrete, when dropped on the pens they punched through 14 feet and exploded the rest of the way, destroying at least 60 E-boats. Cheshire went on to lead Tallboy raids on chemical plants, V-1 launch sites and V-2 rocket storage facilities.

Reports had been arriving about a new secret weapon at Mimoyecques, on the coast near Calais. Photorecon images showed railroad spurs disappearing into hills, as well as spoil heaps, indicating extensive tunneling. Thousands of workers were said to be building vast underground galleries and installing new V-3 guns that were 400-feet long and could fire 300-pound shells up to 100 miles. The barrels and breeches were underground: all that showed on the surface were small steel doors concealing the muzzles, difficult to spot and almost impossible to hit. Two batteries of 25 guns each were under construction—a nightmare artillery nest that would be capable of raining more explosives on London in two weeks than Berlin had seen during the whole war.

Cheshire marked the site on July 6, and in the face of intense anti-aircraft fire that damaged several Lancs, 617 Squadron landed several Tallboy hits, collapsing tunnels and causing extensive underground damage. One of the bombs even scored a bull’s-eye, plunging down a shaft and exploding at the bottom, resulting in Wallis’ earthquake effect. The Germans subsequently abandoned the site, admitting, “The installations were not designed to withstand bombs such as these.”

Besides their famous dambuster raid, No. 617 Squadron's November 12, 1944 mission to sink the German battleship Tirpitz is one of their most memorable. Almost obscured by the explosions of the Lancaster's Tallboy bombs, the Tirpitz meets her fate. (IWM C 4775)

After 100 bombing missions, a protesting Cheshire was told that he had done enough. He was awarded the Victoria Cross, the citation noting his “supreme contempt for danger.” Wing Commander “Willie” Tait took his place, and using Cheshire’s spot-marking method led the squadronagainst the V-2 rocket factory and launch site at Wizernes, France, covered by a 10,000-ton concrete dome. The earthquake effect knocked the dome askew and caused much of the hillside beneath it to collapse. No V-2 rockets would be fired from France. Tait led several more missions against U-boat pens, canals and dams, including the Sorpe on the Ruhr River. Though the Tallboys scored several hits in that sortie, the dam held—the Germans had lowered the water level to reduce the pressure.

Tait’s most memorable achievement before handing over command to Johnnie Fauquire would be against a ship. Lurking in a Norwegian fjord, the battleship Tirpitz posed a constant threat to Allied shipping, especially Artic convoys. The flight to Norway was too far for Tallboy-equipped Lancasters based in Britain, but only 600 miles from Yagodnik, in Russia—just within range of northern Scotland. After harrowing 12-hour flights in foul weather, the Lancs arrived at Yagodnik and nearby fields. Several bombers were write- offs, but the serviceable aircraft took off on September 15 and found the battleship, which was quickly hidden by smoke produced by generators in nearby hills. With the Russian winter closing in, the Lancs returned to Britain.

In November the Germans moved Tirpitz to Tromso Fjord, just within range of Scotland. Twenty 617 Lancasters attacked the battleship on the 12th. This time the smoke generators had not been primed beforehand, but Tirpitz fought back using its 15-inch armament and multiple anti-aircraft guns. Within three minutes, the squadron scored several direct hits and near misses with Tallboys. Then the “C” turret’s magazine exploded, and the great ship slowly rolled over. Like the tunnels, viaducts, bridges, gun emplacements and factories targeted by 617 squadron, the mighty Tirpitz had met its match.

Nicholas O’Dell wrote about the original Dambuster mission in our July 2013 issue. For further reading, he recommends: A Hell of a Bomb, by Stephen Flower; Beyond the Dams to the Tirpitz, by Alan W. Cooper; and No 617 “Dambuster” Squadron by Alex Bateman.

this article first appeared in AVIATION HISTORY magazine

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