Operation Downwood was the official name for the famous attacks on German dams on May 17, 1943 in World War II using a specially developed "bouncing bomb." The Dam Busters were Royal Air Force 617 Squadron.
The Bouncing Bomb
The mission developed out of the bomb. The bomb was designed by Barnes Wallis and developed into a working device by a team at Vickers. Wallis was an aircraft designer and had the successful Wellesley and Wellington to his credit, while working on the Warwick he also began work on bomb design with dams specifically in mind.
His initial idea was for a 10-ton bomb to be dropped from 40,000 feet, but research showed that without a direct hit a bomb would need to be uncarriably vast to breach a dam. However, a much smaller charge would suffice if it could be exploded directly against the dam wall below the surface of the water. But the major German dams were protected by heavy torpedo netting to prevent such an attack and it was Wallis's breakthrough to see a way past this.
A drum-shaped bomb, spinning rapidly and dropped from a sufficiently low altitude at high speed would, for a short distance, skip over the surface of the water in a series of bounces before halting and sinking. An accurate drop could bypass the dam protection and be detonated against the dam with a hydrostatic fuse. After testing and many meetings the idea was adopted on February 26, 1943. The dams were to be bombed in May of that year, when water levels would be highest.
The Squadron
The operation was given to 5 Group and a new squadron was formed to undertake the mission. Initially called Squadron 'X' it was led by Wing Commander Guy Gibson, a veteran of over 170 missions. A further 21 crews were chosen from 5 Group to join the new squadron based at Scampton.
The dams were to be three key dams in the Ruhr area, the Moehne and the Sorpe on the Ruhr River and the Eder Dam on the Eder River. The loss of hydroelectric power was important but the loss of water to industry, cities and canals would be of greater impact.
The Aircraft
The aircraft were adapted Avro Lancaster Mk IIIs, dubbed Special Bs. To reduce weight much of the armour was removed as was the mid-upper turret. The substantial bomb and its unusual shape meant that the bomb doors were removed and the bomb itself hung, in part, below the body of the aircraft. It was mounted in two crutches and before dropping it was spun up to speed by an auxiliary motor.
Bombing from 60 feet at 240 mph, at a very precise distance from the target, required expert crews, intensive night and low-altitude flying training, and the solutions to two technical problems:
- Distance measurement — The two key dams at Moehne and Eder had a tower at each of their ends. A special aiming device (basically a triangle similar to that created by the two towers and an airplane at the correct distance from the dam) showed when to release the bomb.
- Altitude measurement — Two spotlights were mounted under the nose and under the fuselage such that their beams would intersect 60 feet from the underside of the plane. At the correct height, the two spots of light would merge into one on the surface of the water.
The Attacks
The Lancasters were organised into three groups. Formation 1 was to attack the Moehne and after that aircraft still with bombs would attack the Eder. Formation 2 was to attack the Sorpe. The third group was a mobile reserve, it would take off two hours later and bomb as directed.
Formation 1 arrived over Moehne Lake and Gibson's aircraft (G for George) bombed first. Hopgood (M for Mother) attacked second but was hit by flak and destroyed. Martin (P for Peter) bombed third, his aircraft was hit but made a successful attack. Then Young (A for Apple) made a successful run and after him Maltby (J for Johnny) — and finally the Moehne dam was breached.
Gibson then led Young, Shannon, Maudslay and Knight to the Eder. The Eder valley was heavily fogged but not defended. Shannon made several runs before taking a break. Maudslay (Z for Zebra) attempted a run but the bomb struck the top of the dam and the aircraft was caught in the blast. Shannon then successfully dropped his bomb and Knight's final bomb breached the dam.
McCarthy (T for Tom) reached the Sorpe alone. Despite the mist and ill-placed hills McCarthy's aircraft successfully dropped its bomb but did not breach the dam.
Bomb Damage Assessment
The Moehne and Eder lakes poured around 330 million tons of water into the western Ruhr region, mines were flooded and houses, factories, roads, railways and bridges destroyed as the flood waters spread for around 50 miles from the source. In terms of deaths, 1,294 people were killed, 749 of them Russian POWs from a camp just below the Eder Dam.
Of the surviving aircrew thirty-three were decorated at Buckingham Palace on June 22, with Gibson awarded the Victoria Cross. There were five DSOs, ten DFCs and four bars, twelve DFMs and two CGMs. In all, of 133 aircrew, 53 had been killed and three bailed out to become POWs.