The Dams Raid May 1943

	This page:general and timeline.
	Aircraft, teamwork, training, the raid and the men.
	The plan and the actual, results, bibliography, exhibition.

CODENAME - OPERATION CHASTISE

This operation is one of the best known of the Second World War. It involved three key components - the aircraft, the weapon and the aircrew. The Avro Lancaster, designed by Roy Chadwick; the so-called "bouncing bomb" designed by Barnes Wallis and the men of 617 Squadron, Royal Air Force, led by Wg.Cdr. Guy Gibson.

WHERE? The Heartland of Germany - The Ruhr and Weser Valleys.

WHAT? An air attack planned on 6 Dams with the objective of breaching the Dams and thus releasing the water stored in the reservoirs behind them.

WHY?

1. To deprive heavy industry, particularly the steelworks, of their water supply. No water means no steel, which means no weapons nor ammunition.
2. By depriving the canals of their feed water to disrupt the canal network which was used for transporting much of the material to, and output from, the steelworks and armament factories.
3. To disrupt the supplies of hydro-electricity.
4. To disrupt communications by floods damaging roads, railways and canals.

HOW ? A low level precision bombing raid using a new type of weapon - the so-called "bouncing bomb" designed by Barnes Wallis. Codename of this new weapon - "UPKEEP".

WHEN? 16^th /17^th May 1943. At this stage in the War the Allies had had very little success in Mainland Europe, the war in the Far East and the battle of the Atlantic was going badly, though there had been good news from North Africa. Also in May the reservoirs would be full and this was necessary for the "bouncing bomb" to work and full reservoirs would also increase the flood damage to the local transport network.

WHO? The 133 aircrew of the Royal Air Force, and other Commonwealth Air Forces in 19 Lancaster Bombers of 617 Squadron.

PREPARATION

TIMELINE

The idea of breaching the Dams was an idea with a long gestation period. It was also an idea that was not unique to Barnes Wallis.

1937/38

Air Ministry identified Dams as important potential targets, but could see no way of destroying them.

1939/40

Independently, Barnes Wallis starts researching Dams as targets

1940

Wg. Cdr. Finch Noyes suggests that 10,000lbs of explosive detonated next to the Dam wall would breach the Moehne Dam Wallis writes paper " A Note on a Method of Attacking the Axis Powers". Some note; it was 51 pages plus diagrams and appendices, 121 pages in total. Main points -

1. Modern Warfare is entirely dependent upon industry
2. Industry is dependent upon adequate supplies of power
3. Power is dependent upon the availability of natural stores of energy such as coal, oil & water (white coal)

He suggests a 10 ton bomb dropped from 40,000 feet as the way forward. This would be effective against coal mines, dams and other targets. But no aircraft was available that could carry this weight to this height. Bombing accuracy from this height would also have been a problem.

1:50 scale model of the Moehne Dam built at the Road Research Laboratory, Harmondsworth.

Work starts on constructing a 1:50 scale model of Moehne Dam build from millions of small bricks at the Building Research Station at Garston.

1941

Tests continue at BRS, Garston and at RRL, Harmondsworth. Also a 1:10 scale model of the Nant-y-Gro dam in Wales is built at Harmondsworth. The Nant-y-Gro dam is itself 1/5^th the size of the Moehne.

1942

April. Wallis' first marble experiments on the patio in his garden at Effingham, Surrey, followed by catapult experiments at Silvermere Lake near Weybridge. He was looking for an alternative way of placing the required amount of explosive adjacent to the dam wall.

22 April. Wallis produces a paper "Spherical Bomb - Surface Torpedo" which explains the bouncing technique without revealing the need for back-spin. This paper was widely circulated during May.

1 May. First tests at the Nant-y-Gro dam in Wales. The dam held and this suggested that at least 30,000 lbs of explosive would be needed to burst the Moehne Dam if the explosives were detonated away from the Dam wall.

End of May. More experiments at Silvermere Lake.

June/September. Experiments using the ship testing water tanks at the National Physics Laboratory at Teddington.

24 July 1942. Second test at Nant-y-Gro dam to study the effect of detonating the explosives in contact with the Dam Wall on the water side. Success. This showed that only 7,500lbs of explosives would be needed to burst the Moehne Dam PROVIDED that they were detonated in contact with the dam wall on the water side some 30 feet below the water level.

Oct. First air tests of a spinning weapon. Carried out in a Wellington to find out if spinning large bombs while still in the aircraft would affect the handling of the aircraft - it didn't.

4 Dec. First drop of a spinning weapon - from a Wellington off Chesil Beach. Bombs not strong enough.

15 Dec. Second test drops off Chesil Beach. Strengthened spheres damaged but not broken.

1943

9 Jan. Wallis issues his paper "Air Attack on Dams" with the conclusions of the many tests and experiments. 6,500lbs of explosive needed to be detonated against the Dam wall, on the water side at a depth of some 30ft. below the water level.

10 Jan. First successful drop. Sphere bounced.

23 Jan. More success. Wooden cased bomb bounces 13 times.

14 Feb. Air Chief Marshal Sir Arthur Harris, C-in-C Bomber Command, says of Wallis' idea : " This is tripe of the wildest description."

23 Feb. Wallis instructed by the Chairman of Vickers-Armstrong - his boss - to stop all work on the Dams project. He offers to resign.

26 Feb. All systems go. Bombs to be developed and made and the raid to take place by 26^th May at the latest, i.e. in just 12 weeks.

Wallis' reaction: - "I had won my battle and I had the terrible responsibility of making good all my claims and you can't imagine what a horrible feeling that is. When somebody has actually called your bluff. You are depending upon your self confidence and past experience of successes to guarantee that you can do something entirely new, which nobody has ever done before"

At this stage no full size UPKEEP had been made, let alone tested. Indeed there was not even a full set of drawings. After months, or even years, of patience and frustration things now started to move very quickly.

17 March. Squadron 'X' formed.

21 March. Guy Gibson arrives at Scampton to take command of the new squadron.

24 March. Gibson meets Wallis for the first time.

27 March. Squadron 'X' given new identity - 617 Squadron.

29 March. Gibson told the targets.

8 April. First of modified Lancasters arrives at Scampton.

13 April. Scaled down version of UPKEEP dropped at Reculver from a Wellington watched by Gibson. Outer wooden casing burst but the central cylinder continued bouncing. Test drops from a Lancaster as well.

21 April. Wallis recalculates height to drop bomb from as being 60ft. instead of previous estimate of 150ft.

29 April. Full size UPKEEP dropped.

7 May. All leave stopped for all 617 Squadron personnel.

10//11/12/13 May. Some full size, full weight, but inert, UPKEEPs dropped by some 617 Squadron crews.

13 May. First test of full-size live UPKEEP. This was the only time a full size UPKEEP was detonated before the raid. A second live UPKEEP was tested on 15 May but it was, purposely, not detonated.

Through the many trials and experiments Barnes Wallis was able to demonstrate that the dams could be breached provided a sufficiently large amount of explosive was detonated adjacent to the Dam wall, on the water side and at a depth of about 30ft below the water level. He was also able to demonstrate that he had designed a weapon that could do the job. The weapon, which was really a depth charge, had to be dropped from a low level in order to bounce. It had to bounce so that it would jump over any anti-torpedo nets and so that it could be placed right up against the dam wall. It had to be spun before it was dropped in order to increase the likelihood of it bouncing, to increase the length of each bounce and to make it slide down the dam wall rather than rebound away from it.

© Peter Rix, Barnes Wallis Memorial Trust

	This page:general and timeline.
	Aircraft, teamwork, training, the raid and the men.
	The plan and the actual, results, bibliography, exhibition.