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.


The Heartland of Germany – The Ruhr and Weser Valleys.


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.


To deprive heavy industry, particularly the steelworks, of their water supply. No water means no steel, which means no weapons nor ammunition.
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.
To disrupt the supplies of hydro-electricity.
To disrupt communications by floods damaging roads, railways and canals.


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“.


16th /17th 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.


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


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.


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


Independently, Barnes Wallis starts researching Dams as targets


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 –

Modern Warfare is entirely dependent upon industry
Industry is dependent upon adequate supplies of power
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.


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 1/5th the size of the Moehne.


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.


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 26th 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.


The only aircraft capable of carrying the final version of the new weapon was the Avro Lancaster, and even this needed several modifications. The main modifications were :-

Remove mid-upper turret to save weight and reduce drag
Remove bomb bay doors – UPKEEP was too large to fit into the bomb bay
Cut away fuselage to accommodate UPKEEP
Install hydraulic motor to spin UPKEEP
Install two Aldis Lights used to determine correct height.
Install VHF radio sets
Install stirrups for front gunner to keep his feet away from bomb aimer
Install second altimeter on windscreen so that pilot did not have to look down at instrument panel – an early version of the now common head-up display principle


All bomber operations called for strong co-operation between the crew-members, but this raid had an even greater than usual requirement for teamwork.

During the final approach special responsibilities were:-

Pilot -direction
Navigator -height
Flight Engineer -speed
Bomb Aimer -distance
Wireless Operator -spinning the weapon
Front and rear gunners -defence

A further consideration was that most bomber crews had very little experience of low level flying, and certainly not at the extremely low levels required on this operation.
Intensive training was required.


The aircrews had to practise flying, and navigating, at low level and over water. Initially they used standard, unmodified, Lancasters borrowed from other Squadrons.

One of the locations used for the training flights was the Eyebrook Reservoir in Rutland. The most well known training ground was the Derwent valley, near Sheffield.


15 May. Order from Bomber Command – “Operation Chastise. Execute at first suitable opportunity.”

Final list of Dams to be attacked :
Moehne codeletter X
Sorpe Z
Lister D
Ennepe E
Eder Y
Diemel F

15 May.
16.00 Wallis arrives at Scampton
18.00 Flight Commanders briefed

16 May.
Morning and afternoon. Specialist crew briefings.
18.00 Final briefing of all aircrew.
21.28 First aircraft takes off.

The raid was a lot more complicated than simply 19 aircraft taking off, flying to their targets, dropping their weapons and then returning


There were 19 aircraft, each with a crew of 7 – a total of 133 men. They came from many countries:

British (RAF and RAF(VR)),
(including one Australian) 90
RCAF (including one American) 29

Summary of awards.

1 Victoria Cross
14 DFC or Bars to DFC
12 DFM or Bars to DFM

a) The Plan

Three waves. Routes out and back planned to avoid known areas of flak. Fly at low level so that it would be difficult for the aircraft to be spotted and difficult for them to be attacked by night-fighters.

First Wave – Three sections each of three aircraft. Take Southern Route. Target Moehne Dam, once that is breached remaining aircraft to attack Eder Dam and when that is breached any aircraft still with their weapon on board to attack the Sorpe Dam.

Second Wave – Five aircraft. Take the longer, northern, route. Target Sorpe Dam. So that this wave would cross the enemy coast at the same time as the first wave it took off about 10 minutes before the first wave.

Third Wave. Five aircraft. Southern Route. Airborne reserve under control of Group HQ. Took off 2 1/2 hours after waves 1 & 2 to allow its aircraft to be recalled before crossing enemy coast if waves 1 & 2 were successful in destroying all the dams.

b) The actual

Some indication of the complexity of the operation can be gained by looking at the position of all the aircraft at certain key points in time.

Some of the information is only approximate because surviving records are incomplete. Also, to quote the official report of the operation “As a whole the logs returned do not show as high a standard as they do on a normal high level night sortie”. There were, of course, very good reasons for this.

At 22.56.The first aircraft crossed the enemy coast. This was Munro in AJ-W. Just one minute later the first loss occurred when Byers in AJ-K crashed. Waves 1 & 2 crossed the enemy coast at about the same time but a hundred miles apart. The third wave aircraft were still on the ground at Scampton.

At 00.28. the first aircraft attacks the Moehne Dam. This was Gibson in AJ-G. By this time one of the aircraft in the first wave had been lost – Astell in AJ-B. As well as Gibson the remaining aircraft of the first wave were now in the vicinity of the Moehne – 8 in all.

At 01.52. The last attack on the Eder Dam – about the same time as third wave crosses enemy coast.

At 03.11.The first attacking aircraft landed back at Scampton.


TIME 22.56 DBST ( Double British Summer Time)
First aircraft cross the enemy coast

1st wave of 9 aircraft crossing enemy coast – southern route – target Moehne and Eder
2nd wave of 5 aircraft crossing enemy coast – northern route – target – Sorpe
3rd wave of 5 aircraft still at Scampton – target – as needed.


Very soon after the first aircraft crossed the enemy coast the first crash occurred.
AJ-K, Byers, crashed at 22.57.

AJ-W, Munro, was damaged by flak and had to return to base.

AJ-H, Rice, flew so low it hit the water and its UPKEEP was ripped off. This aircraft returned to base.

AJ-E, Barlow, crashed at 23.50

AJ-B, Astell, crashed at 00.15

The 5 aircraft of the third wave took off between 00.09 and 00.15.


TIME 00.28
‘G’ – Gibson – attacks Moehne

8 aircraft, all from first wave- are in the vicinity of the Moehne,
1 aircraft of first wave had crashed
2 aircraft of second wave had crashed
2 aircraft of second wave were nearing Scampton having had to return early due to problems
1 aircraft of second wave was in the vicinity of its target – the Sorpe
5 aircraft of third wave had taken off 13-19 minutes previously


AJ-M, Hopgood, was shot down during the attack and crashed after dropping his UPKEEP at the Moehne.

5 aircraft from first wave fly on to the Eder after the attack on the Moehne. 2 aircraft from the first wave head for base.

AJ-T, McCarthy, attacked the Sorpe at 00.46 and headed back to base.

Third wave has now crossed the enemy coast.

TIME 01.52 Last attack on the Eder
Of the 8 aircraft of the first wave which had been in the vicinity of the Moehne one had crashed immediately after attacking the Moehne; two were on their way back to Scampton and the remaining 5 flew on to the Eder (but only three of these still had their UPKEEPS)
Of the 5 aircraft in the second wave 2 had crashed; 2 had returned early to Scampton; 1 had attacked the Sorpe at 00.46 and was now on its way back to Scampton.
The 5 third wave aircraft had crossed the enemy coast about 20-25 minutes previously.
Of the 19 aircraft which had left Scampton, 2 had returned early; 4 had crashed and 13 were still in the air.


AJ-S, Burpee, crashes at 02.00

AJ-A, Young, crashes at about 02.30.

AJ-C, Ottley, crashes at 02.35

AJ-Y, Anderson, has navigational difficulties and at 03.10 Anderson decides to abandon the mission and turns back to base.

The remaining aircraft of waves 1 and 2 head for base having dropped their UPKEEPS.

TIME 03.11 First attacking aircraft lands back at Scampton
By this time;
2 aircraft had returned early
8 had crashed
1 had just landed
3 others were less than 20 minutes flying time away
2 were on their way back, still about an hour flying time away.
2 were still in the vicinity of the dams and were about to attack
1 was still over Germany but heading for home due to navigational problems and without having attacked.5 aircraft attacked the Moehne
3 aircraft attacked the Eder
2 aircraft attacked the Sorpe
1 aircraft reported that it had attacked the Ennepe


Chastise Aircraft Summary

Chastise Aircraft Summary


Two dams breached – The Moehne and the Eder. One dam damaged – the Sorpe – such that the German authorities lowered the water level in the reservoir to reduce the risk of the Dam giving way. 11 factories destroyed, 114 damaged. 25 bridges destroyed, 21 damaged. Electricity, water and gas supplies interrupted. Approx 1300 casualties. Rationing tightened.
Other consequences – 10,000 German forces dedicated to defending similar targets; Workers redeployed from building the Atlantic Wall to repairing the Dams and the damage done by the raid.
The effect on morale, on each side, was enormous. This raid seemed to be the start of the fight back. Leaflets describing the raid were dropped on Occupied territory. The effect on relations with US and Russia was also significant – Russia was pressing for the opening of a Second Front to relieve pressure on its forces; America was considering giving priority to the war in the Far East. Churchill used the success of the Dams Raid to smooth relations with Britain’s allies.


The Dambusters Raid- John Sweetman. A thoroughly well researched study both of the raid itself and the events leading up to it. This book has been published in various editions, the latest in 2003 and this contains extra chapters bringing the story up to date. Even now new information is coming to light.

The Men who Breached the Dams – Alan Cooper. Particularly good, as might be expected from the title, on details of the men who flew on the raid giving details of the service history of each man. Also an interesting summary of the fate of each of the 19 aircraft which took part in the raid.

The Dambusters – John Sweetman with David Coward and Gary Johnstone. Published in 2003 to accompany the Channel 4 Television programmes. Many photographs and maps. Not as detailed as Sweetman’s other book but very readable.

Enemy Coast Ahead – Guy Gibson. First published in 1946. Only about 20% covers Gibson’s time with 617 Squadron. The rest of the book covers his earlier career with the RAF. A new edition was published in 2003 using Gibson’s original, unedited, words.

The Dam Busters- Paul Brickhill. This is the book on which the 1955 feature film was based. The book, like Gibson’s, suffers a little in that much important information was not available to be published at the time they were written. The book also covers the later work of 617 Squadron.

For more information about the Barnes Wallis Memorial Trust see thier website .