Publication: Air Power History
Publication Date: 22-JUN-05
Format: Online - approximately 9269 words
Delivery: Immediate Online Access
Author: Webster, T.M.
Article Excerpt
At 2128 hrs on May 16, 1943, the first aircraft of the newly-formed 617 Squadron lifted from RAF Scampton's runway and set course for Germany. So started Operation CHASTISE, an attack that had been in planning on and off since October 1937, (1) and that would be recognised as Bomber Command's most spectacular operation of World War II. By dawn the next day two major German dams had been breached, significant areas flooded, more than 1,250 deaths caused, and the Ruhr Valley's industry disrupted. The British force lost eight aircraft and fifty-three aircrew.
The British would use post-raid reconnaissance pictures to show their Empire, their American allies and, using leaflet drops, Occupied Europe the damage caused to the dams, the countryside below them and, by implication, the industrial complex of the Ruhr Valley.
The understandable wartime use of the raid for propaganda purposes may have led to overstatement of its success. The publication of Webster and Frankland's review of the air offensive against Germany brought a re-evaluation which, while acknowledging the attack's precision, held that the physical outcome was neither "of fundamental importance nor even seriously damaging". (2)
This article examines the context of, and build up to, the Dams Raid, recounts the raid itself, assesses the damage directly caused and the German response to it, outlines the lessons that were or could have been learned from the raid, and finally places the raid in perspective.
The Background to the Raid
Contrary to popular belief, the Dams Raid's origins did not lie with Barnes Wallis, the Vickers' engineer who designed the "bouncing bomb." (3) As early as October 1937, Air Ministry planners were developing attack options for the expected war with Germany: the thirteen Western Air (WA) Plans. Plan WA5 required Bomber Command "to attack the German War Industry including the supply of oil with priority to that in the Ruhr, Rhineland and Saar." (4) Bomber Command refined this into a plan to achieve the same effect by attacking the Ruhr's forty-five power and coking plants: it was believed these could be destroyed in a fortnight's bombing (about 3,000 sorties) at an expected aircraft loss rate of about 6 percent. That these estimates were wildly inaccurate was shown by the 11.5 percent loss rates of the RAF's then-heavy bombers in the period of the Phoney War (5) and the Butt Report's conclusions on Bomber Command's accuracy (6) which, taking no account of the doubtful effectiveness of the bombs with which the RAF started the war, suggested that 12,000 sorties would have been required. Extrapolating these figures, a loss of approximately 1,400 aircraft might have been expected.
Even on the original estimates, the loss rate for the new plan was considered unacceptable and the Air Ministry looked for alternative means to the same end: the result was a plan to attack the Mohne and Sorpe dams. This plan argued that the Ruhr's heavy industry was dependant on the water the dams held for industrial processes, for power generation and for drinking water: if the dams could be destroyed then industry would grind to a halt. Assuming the logic contained no flaws, the next step was to identify a way to attack the dams. Considerable effort went into this, concentrating particularly on the Mohne gravity dam. (7) Suggestions included attacking the air-side of the dam with semi-armour piercing bombs, dropping high-explosives onto the dams or attacks with multiple torpedoes from the water-side. None of these was considered feasible and a guided-bomb based upon an anti-aircraft target drone was considered the best option. Unfortunately, the fall of France placed the target out of the range of such a weapon.
Even before the fall of France Wing Commander Finch-Noyes of the Woolwich Research Department was working on alternative means for attacking the Mohne dam. After reviewing the extant papers, he proposed that a 20,000-lb. explosive charge detonated 40 feet from the top of the dam on its water-side and in contact with it (or a succession of 2,000-lb charges close together) would have a reasonable chance of destroying it. His proposed weapon would be launched from an aircraft at low level, propel itself into the dam, sink and then be exploded by hydrostatic fuses at the desired depth. (8) No single weapon could be used, no RAF aircraft was yet capable of delivering it to the target, and so multiple smaller weapons would have to be substituted. The Wellington bomber could carry a 2,000-lb. charge weapon under each wing to be dropped at height and distance from the dam and, with the weapon propelling itself after hitting the water, skip over any intervening torpedo nets, strike the dam, sink and explode. Finch-Noyes proposed to use a total of sixteen weapons, but Bomber Command decided that this plan was fraught with technical imponderables and it was quietly shelved. Before the Dams Raid took place, other means of attack were put forward: Combined Operations suggested floating a charge down the reservoir and onto the dam, while the Special Operations Executive proposed an attack by parachutists, who would place explosive charges against the dam. (9)
Weapon Development
Work on the design of the weapon to be used on the Dams Raid started in the autumn of 1939. The man behind it was Barnes Wallis, an aero-structures engineer with Vickers-Armstrongs' Aviation, already well known for his work on the R100 airship, and the Vickers Wellesley and Wellington bombers. Wallis believed that modern warfare depended on industrial production which, in turn, relied on sources of power. He argued that production could be dispersed, making it relatively invulnerable to the bombs then available to the RAF, but sources of power like coal mines, oil fields, and hydroelectric dams could not. They were, however, equally invulnerable to the RAF's available bombs. (10) Wallis believed that much heavier bombs could be effective and had started to work, with the blessing of the Ministry of Aircraft Production (MAP), on a massive 22,000-lb. bomb, similar in shape to his R100 airship, (11) the bomb was expected to achieve supersonic speed in its fall from altitude. This would be suitable for these targets as it buried itself deep in the earth before exploding, causing shock-waves that would shake structures apart: the same effect could be achieved by exploding the bomb in the water close to a dam.
In autumn 1940, experiments started to determine how much explosive needed to be detonated at what distance from the Mohne dam to destroy it. Initial experiments were on 1:50 scale models, working upwards to progressively larger models and eventually a one-off test on the disused Nanty-Gro dam near Rhayader, which on July 24, 1942, (12)) proved conclusively that such dams could be destroyed by an underwater explosion in contact with the dam. The early model tests gave Wallis the information needed to support his "A Note on a Method of Attacking the Axis Powers." (13) He argued that his massive bomb dropped from high altitude would be effective against the Mohne dam, but no RAF bomber was capable of carrying it to the required altitude. The project ran in parallel with a proposal for an equally large bomber to deliver it. The Air Staff rejected both.
Wallis was not to be put off. Somehow, in June 1941, he gained the support of MAP's Aerial Attacks against Dams committee for further experiments on the effects of explosives on dams. Progress was slow: Wallis himself admitted, "conviction that my original suggestion was impracticable..... led me to seek for other methods." (14) Early in 1942, he hit upon the idea of ricocheting a spherical weapon across the surface of the reservoir thus avoiding torpedo nets and other surface defences, striking the dam, sinking, and then exploding in contact with it at a predetermined depth thanks to hydrostatic fuses. Wallis could not account for how he got the idea but there are similarities to Finch-Noyes' earlier plan.
By the end of April 1942, Wallis had gained important support from Professor Blackett, a scientific adviser to the Admiralty, and from Sir Henry Tizard, who had influence with the Air Council, MAP and the Chiefs of Staff Committee. Their support gained him access to the National Physical Laboratory's water tanks to perfect the delivery technique that now included backward rotation of the weapon. Wallis claimed three advantages for this: "it increases the distance which the missile will travel after release from the carrier, before striking the water; it diminishes the tendency of the missile to plunge downwardly on impact with the water surface; [and] it increases the distance which the missile will travel whilst ricocheting." (15)
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NOTE: All illustrations and photos have been removed from this article.
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