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The Dam Busters

On the night of the 16 May 1943, 133 men in 19 modified Lancaster bombers set out with a new weapon, Barnes Wallis’s bouncing bomb. They were to strike deep into Germany’s industrial heartland and target the dams of the Ruhr Valley. For this, the men of 617 Squadron would go down in history as the Dam Busters.


Barnes Wallis was the Assistant Chief Designer at Vickers Aviation.

He wanted to bring an end to the war with Germany as quickly as possible and firmly believed that striking at Germany’s sources of power would cripple its industry and hence its ability to wage war.

To this end, Wallis had developed the idea of a bouncing bomb. Dropped at distance from the target, the rotating bomb would bounce across the surface of the water and in theory over any protective anti-torpedo nets, before sinking and exploding.

A smaller bomb, codenamed Highball, was designed to be dropped by mosquito aircraft and used as an anti-shipping weapon.

The Admiralty were very keen to develop Wallis’s bomb, specifically for use against the German battleship Tirpitz which was known to be hiding out in the Norwegian fjords. However, the operation, codenamed Servant was canceled.

Upkeep was a much larger bomb. Germany’s industrial heartland was in the Ruhr and its dams were essential to war production. Their destruction would cause vast amounts of damage, cut off an important source of power and disrupt Germany’s war industries.

The Air Ministry had already looked into the feasibility of bombing the Ruhr dams back in 1938 but at the time they could come up with no viable plan. Wallis’s bouncing bomb would spin down the side of the dam and detonate beneath the surface of the water at its base, causing a breach in the wall. This meant the bomb needed a smaller explosive charge which made it light enough to be carried by a Lancaster bomber.

Trials at the Fleet, a lagoon behind Chesil beach in Dorset in December 1942 and January 1943 had shown that the bouncing bomb could work in practice.

However, the Ruhr was deep in enemy territory and heavily defended. The aircraft would need to fly in low, at night and drop the bombs with considerable accuracy – which at the beginning of 1943 was a tall order.

The best time to conduct the attack was in May when the water level behind the dams was at its peak, making a breach more likely. Time was of the essence.

The plan required specially modified Avro Lancaster bombers and the bomber crews would need to be trained for the mission.

Air Marshal Sir Arthur Harris, Commander in Chief of Bomber Command, considered Wallis’s plan for attacking the dams with a bouncing bomb to be “tripe of the wildest description” with no chance of success.

It wasn’t until the end of February 1943 that the Air Ministry finally gave its approval for the development of Upkeep.

Chief of the Air Staff, Air Chief Marshal Sir Charles Portal wanted every effort made to ensure the raid on the Ruhr dams would go ahead in 1943.

The 26 May was the last possible date on which the raid could be carried out. Beyond this date, the water levels in the dams would fall too low and the bombs would not be as effective. That gave them less than three months in which to prepare.

617 Squadron

A special squadron was formed at RAF Scampton, near Lincoln, on 17 March 1943 under the command of Wing Commander Guy Gibson.

The men, most of whom were volunteers came from 5 Group, with the first of them joining the Squadron at the end of March.

Training began in full on the 31 March, although new crew members were still arriving and the first of the modified Type 464 Lancaster bombers would not be ready until the end of April.

Due to the extreme security surrounding the operation, the exact nature of the mission was kept secret. Most of the crew wouldn’t know their targets until the day of the attack. Rumours abounded that it was to be the German battleship Tirpitz.

Gibson devised an intensive training programme that included lots of low altitudes and night flying.

The crews practiced the final approach and dropping of the bomb at Derwent Reservoir to the south of Sheffield and at Wainfleet in the Wash. Dummy runs of the operation were carried out with Eyebrook Reservoir in Northamptonshire and Abberton Reservoir near Colchester standing in for the dams.

It was no mean feat to fly a thirty ton Lancaster with a 102ft wingspan at such low levels. Wallis’s bomb had to be released at a height of 60ft at a distance of 400-450yards from the target and with the aircraft traveling at 230mph. Judging the height of the aircraft over the water proved difficult.

In the end, they solved this problem by attaching two Aldis lamps to the bomber. The two spotlights would converge to make a figure of eight when the aircraft was flying at 60ft.

Trials of Upkeep began on the 13 April off the Kent coast at Reculver.

The last trial was on the 13 May just three days before the raid took place. Wallis’s initial design was for a spherical bouncing bomb but during testing, this had evolved into a cylinder. It had a wooden outer-casing held together with steel bands which were designed to minimize the impact of hitting the water. This was to protect the inner steel casing which held the bomb itself, around 7000lbs of explosives.  Three hydrostatic fuses would fire and detonate the main bomb.

Due to the operational requirements and weight of the bomb, the fuselage of the Lancaster bombers had to be strengthened and more powerful engines installed.

Upkeep was held in place by a specially designed frame but due to its size it still protruded out from underneath the aircraft.

Loading was difficult even with the specially modified bomb bays and the sheer mass of steel used in Upkeep’s construction affected the on-board compass, which had to be compensated for.  The bomb itself had to be carefully balanced to prevent any vibration as it needed to be spun up to 500rpm ten minutes or so before it was released.


Three primary targets were decided upon. The Möhne (Target X), the Eder (Target Y) and the Sorpe (Target Z).

If these three dams were successfully destroyed then the bomber crews with remaining Upkeeps were to go on and attack the secondary targets, the Diemel, Ennepe and Lister dams. The raid was set for the night of Sunday 16 May. It was to be a full moon with clear skies.

There were to be three waves of attack. The first wave consisted of nine aircraft in three groups and would be led by Wing Commander Gibson. Their targets were the Möhne and Eder dams. The second wave was to attack the Sorpe dam. They would cross the Dutch coast at the same time as the first wave but 130 miles further north. The third wave was the reserve wave and they would take off two and a half hours later. The final briefing was at 18.00 and the first planes took off at 21.28.

The Dutch coast was heavily defended. The Lancaster bombers flew at a hundred feet or less to avoid detection from enemy radar and make them harder targets for searchlights and anti-aircraft guns. Flying so low they had to watch out for power lines. It was important to stick to the planned routes which tried to avoid fighter aircraft bases and heavily defended areas.

At 22.50 the leading aircraft of the first and second waves were approaching the Dutch coast.

In the second wave, W-Willie was hit by flak forcing Flight Lieutenant Munro to return to base. Pilot Officer Rice also had to return to RAF Scampton in H-Harry after they lost their Upkeep and took on water while flying too low over the North Sea.  K-King came under fire at Texel and the aircraft went down with no survivors. All seven men of E-Easy were killed when their Lancaster crashed after flying into electrical power lines. Only one aircraft of the second wave, T-Tommy, was left.

The first group of three aircraft in the first wave encountered heavy flak as they approached the Ruhr. So much so that Wing Commander Gibson broke radio silence to warn his crews.  Flight Lieutenant Astell in B-Baker flew into an electrical power line near Marbeck. The aircraft crashed and the Upkeep exploded leaving no survivors.

Five aircraft had now been lost before they’d even reached the dams.


Wing Commander Gibson in G-George carried out a dummy run before making the first attempt on the dam.

Under heavy fire, the Upkeep was released and exploded but much to Gibson’s disappointment the dam wall had not been breached.

M-Mother went next but during their run, the Lancaster was hit by a shell. With the aircraft on fire Flight Lieutenant Hopgood ordered the Upkeep dropped. It bounced over the dam wall and hit the power station below destroying it. The crew began to bail out but only two of the men, John Fraser and Anthony Burcher survived to become POW’s.  A third man, John Minchin bailed out but died of his wounds.

P-Popsie made the next run on the dam with Gibson flying alongside to try and draw away some of the enemy fire. The Upkeep hit the dam but it still had not been breached.

Squadron Leader Young flew the fourth run in A-Apple. Gibson again tried to draw the enemy fire while Flight Lieutenant Martin in P-Popsie fired on the German defenders. The Lancaster’s guns had been loaded with only daytime tracer bullets which gave the illusion of a heavier weight of fire.

Flight Lieutenant Maltby in J-Johnny flew in and released the fifth Upkeep. It was a perfect strike. The wall of the dam collapsed sending a torrent of water into the Möhne valley.


P-Popsie and J-Johnny headed for home. Five aircraft from the first wave flew south-east towards the Eder dam. They had three Upkeeps left. Gibson in G-George and Young in A-Apple had both dropped their bombs but Gibson wanted to lead the attack and Young accompanied in support. The hills and mist covered valleys made it difficult terrain to fly over at such low altitudes.

The Eder was undefended but difficult to attack from the air due to the steeply wooded hillsides and several attempts were made to get the aircraft in low enough to drop the bomb.
L-Leather’s Upkeep hit the wall and exploded with no obvious damage to the dam.

Flight Lieutenant Maudslay took the second run in Z-Zebra. The Upkeep was dropped a fraction too late and it hit the top of the dam and exploded right behind Maudslay’s Lancaster. All contact with the aircraft was lost. Probably damaged by the explosion they attempted the journey home. The plane crashed with no survivors after being hit by enemy ground fire at Emmerich. Flight Lieutenant Knight in N-Nuts had better luck. Their Upkeep caused a large breach in the dam which flooded the Eder valley.

The remainder of the first wave headed for home.  A-Apple was brought down by enemy fire and crashed into the North Sea just off the Dutch coast. All seven of the crew were killed.
Second Wave – Sorpe

Flight Lieutenant McCarthy in T-Tommy reached the Sorpe dam. They were the only aircraft of the second wave to make it.

The Sorpe was not a concrete and masonry gravity dam like the Möhne and Eder, but an earthen dam with a concrete core. The Sorpe’s construction would make it the hardest to breach. The Upkeep was not spun and due to the surrounding terrain, it would have to be dropped while the Lancaster was flying parallel to the dam wall. The topography also made getting down to 60ft very difficult. It was on the tenth run at 12.46am that they managed it.

The Upkeep detonated sending a massive column of water and debris into the air but the dam held. T-Tommy headed for home and made it back to RAF Scampton despite being damaged by shellfire on the return journey.
Reserve Wave

The five planes of the reserve wave had left RAF Scampton shortly after midnight.

S-Sugar strayed off course and went down near the Gilze-Rijen airfield. All the crew were killed.

C-Charlie came under fire near Hamm. The Upkeep exploded but the tail gunner Flight Sergeant Fred Tees managed to survive the crash, the only member of the crew to do so.

Flight Sergeant Brown in F-Freddie managed to reach the Sorpe dam but encountered the same difficulties with the approach as McCarthy had in T-Tommy. After several attempts to get it right, they released the Upkeep but it did not destroy the dam.

Brown made it back to RAF Scampton even though his Lancaster was hit by ground fire on the return journey. Pilot Officer Anderson in Y-York had got hopelessly lost and with daylight fast approaching had decided to head for home without dropping their Upkeep.

At 3.37am O-Orange dropped their Upkeep which exploded just short of what they believed to be the Ennepe dam (although it may have actually been the Bever dam) but did no damage. Flying on three engines they were the last to arrive back at RAF Scampton at 6.15am.

Eleven of the nineteen crews had returned. Of the 133 men who took part in the raid 53 were killed and 3 were taken prisoner.


The Sorpe had held, but the Möhne and Eder dams had been breached, draining their reservoirs. In the Möhne and Eder valleys, vast swathes of devastation had been left by a wall of water and debris some ten metres high.

There was heavy damage to the infrastructure, with no bridges for miles. Many power stations and factories had been destroyed or were out of commission and several large towns were temporarily without water.

The German High Command was determined to rebuild the dams as soon as possible. It was an immense undertaking requiring vast resources and manpower that had to be diverted from elsewhere.

The rebuilding of the Möhne and Eder was well underway by the beginning of July and they were officially opened on the 3 October 1943.

Post war there has been heavy criticism of the effectiveness of the Dam Buster raid in part because the dams were rebuilt so quickly. There are also questions over why Bomber Command did not follow up with conventional high altitude bombing raids while the dams were being repaired.

At the time the raid was a huge morale boost and a great propaganda opportunity for Britain. Pictures of the flooded valleys soon appeared in national and international newspapers.

34 members of 617 Squadron were awarded medals at a ceremony at Buckingham Palace. For his part, Wing Commander Guy Gibson was awarded the Victoria Cross.