The following article on the Dam Busters is an excerpt from The Hunt for Hitler’s Warship © 2015 by Patrick Bishop. It is available now from Amazon or Barnes & Noble.

The Dam Busters — officially No. 617 Squadron — were an RAF squadron who gain the name for their actions in World War Two during Operation Chastise against the German dams. The squadron was formed specifically to attack three major dams that provided power and water to the Ruhr industrial region of Germany. Breaking the dams would cripple the industrial might of the Nazi War machine. During the Second World War the Dam Busters carried out nearly 1,600 operational sorties, losing nly 32 aircraft.


Nearly as famous as the squadron were the weapon they used. In the spring of 1943 a new weapon appeared which promised to succeed where conventional bombs—and the hopeless spherical “roly-poly” mine—had signally failed. Its creator was Barnes Wallis whose bouncing bomb was dropped by the Dam busters on their spectacular raid of May 16–17. The new invention, code-named “Highball,” was based on the same principle. It was cylinder-shaped, weighed half a ton, and contained a 500-lb. charge.

Their most famous operation was Operation Chastise, an attack on German dams, carried out on May 16-17, 1943. Their “bouncing bombs” breached the Mohne and Edersee Dams, flooding the Ruhr valley and villages in the Eder valley. In the wake of the flooding, two hydroelectric power plants were destroyed, along with factories and mines. Over 1,600 civilians drowned: approxmiately 1,000 Soviety forced-laborers and 600 Germans. German war-time production was severely hampered until September.

The squadron chose a badge that depicted the bursting of a dam and a motto Apres moi le deluge (After me, the Flood).

The squadron continued in precision bombing raids throughout the war. But they needed a better bomb than their bouncer. Thus came in another revolutionary weapon: Tallboy.

Tallboy — The Preferred Weapon of the Dam Busters

The Tallboy was the latest invention of Barnes Wallis, a creative engineer, and in the words of his friend and biographer J. E. Morpurgo “saw creative engineering as an art and himself as a sort of poet.” In the crucible of wartime, his prodigious talent and energy had produced some remarkable and valuable inventions.

The idea for the Tallboy dated back to 1940 but Wallis had only been put to work on developing it in the summer of 1943, when it was discovered that the Germans were close to deploying flying bombs and long-range ballistic missiles—the V1s and V2s. The only defense available was to bomb the sites where they were being developed or stored. A mass raid by nearly six hundred aircraft dropped 1,937 tons of bombs on the V2 missile research center at Peenemünde on the Baltic coast on August 17, 1943. This was a huge attack, but forty aircraft were lost and the program was set back by only two months. The blunt instruments that were all Bomber Command had available could not do the job. Something more precise and deadly was required.

Wallis had foreseen the need for a bomb for use against “targets . . . of the most massive nature . . . practically invulnerable to attack by existing aerial methods.” It was axiomatic that the bigger the bomb, the greater its destructive potential, but in the first years of the war, aircraft lacked the lifting power to carry monster weapons. With the arrival of the Lancaster, capacity increased. Tallboy was not just a very big bomb; it was designed to bury itself in the ground and explode, producing an earthquake effect. Shockwaves ripple more powerfully through earth— and water—than they do through air. Thus, a Tallboy did not have to score a direct hit to destroy its target.

To achieve the penetration needed for the best results, the bomb had to be dropped from high altitudes. It needed to be tough and aerodynamically efficient to withstand the impact. Wallis’s bomb was made of molybdenum steel, sufficiently strong and light to carry a high proportion of explosive—5,000 pounds of Torpex in an all-up weight of 12,000 pounds It was twenty-one feet long, tapering to a point that was as sharp as a pencil and fitted comfortably into the Lancaster’s thirtythree-foot bomb bay. According to its inventor, “previously bombs had just [been] made [of] thin steel casings which dropped from the sky. But I gave this bomb [a] perfect aerodynamic shape and arranged the fins so they would impart to it an increasingly rapid spin. As the bomb attained a high velocity it actually passed through the speed of sound and penetrated the ground to a depth of about a hundred feet.”

The loss of accuracy that grew with increased altitude was offset by the use of the Stabilized Automatic Bomb Sight (SABS). With conventional sights, the bomb aimer had to guide the pilot up to the moment of release. The delay between instruction and adjustment left an inevitable margin of error. The SABS was the most sophisticated aiming device to date. Shortly before arrival at the objective the navigator passed data on airspeed, altitude, and wind direction to the bomb aimer, lying in the nose of the aircraft, to be fed into the instrument’s computer. He then peered through the lens of the sight, speaking into the captain’s earphones, calling “left, right, steady” as needed until the target lay at the tip of a lit-up sword symbol reflected on a sheet of glass. As the target grew closer he held it in place, sliding down the blade of the sword, with two control wheels. These activated an instrument mounted in front of the pilot—the Bombing Direction Indicator. A needle on the face then told him the slight adjustments needed to keep the aircraft on track. Then, at the optimum moment, the bomb was released automatically. An experienced aimer could drop a bomb from 20,000 feet with an average margin of error of only eighty yards. To do so, of course, he needed to have clear sight of the target. Over cloud—or smokescreen— the SABS was useless.

The Dam Busters and the Sinking of German Battleships

Throughout the summer of 1944, 617 Squadron had been using both Tallboy and the SABS in specially modified Lancasters against V weapons sites buried deep under concrete in the Pas-de-Calais. In the month of August, prior to the summons to prepare for a “special job” they had repeatedly and successfully bombed the previously invulnerable submarine pens at the Biscay ports of Brest, Lorient, and La Pallice.

Using the Tallboy, their most notable attack was the sinking of the German warship Tirpitz. The ship reguarily threatened Allied Arctic convoys in northern Norway. After being damaged by British midget submarines and attacks from the Fleet Air Arm, the No. 9 and No. 617 Squadroms were deployed to finish Tirpitz off with Tallboy bombs. The two squadrons harrassed her throughout 1944 and finally sunk her on November 12 when aircraft scored two direct hits in quick succession. All three RAF attacks on Tirpitz were led by Wing Commander J.B. “Willy” Tait.

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