The Dambusters were an elite group of Royal Air Force bomber crews, selected for a unique mission, with a unique weapon, in order to "have a chance to hit the enemy harder, and more destructively, than any small force has ever done before!".
He focused his attention particularly on the large water dams of the Ruhr valley, Germany's main steel production area, and steel is essential for military production. The dams provided electric power, and vast amounts of water, essential for steel production and for the transportation waterways which served it.
His original idea, used later in the war, was to produce huge 10 ton bombs with strong steel casing, to be dropped from very high altitude so that they would reach the ground at supersonic speed, penetrate many meters into the ground, and explode there. Even if they near-missed the target, the massive underground exlosions would instantly create large caverns and send shockwaves to the foundations of the target structure, causing it to collapse as if hit by earthquake. Wallis called it "Earthquake bomb".
With 21st century precision-guided bombs, it's much easier, but in 1943, it was impractical, until Wallis came up with the idea of bouncing a massive bomb on the dam's lake surface, like a child bouncing a pebble on water, so that the bomb would bounce over the torpedo nets, hit the dam wall and sink there into the water, and only then explode, triggered by a water pressure fuze, not by impact.
This meant that a heavy bomber, flying very low and fast over the dam's water lake, at night (or it would be shot down for sure by the German defenders), at precisely the right altitude, at precisely the right speed, and drop the bomb at precisely the right distance from the dam wall, could do it. That seemed almost as impractical, but while the laws of physics could not be bent, elite bomber crews could perhaps be especially trained to do just that, at night, and under enemy fire.
The squadron's pilots quickly realized that they cannot achieve the required precise altitude and distance without proper means of measurement, but that was solved by equipping the bombers with precisely mounted downward spotlights, set so that their light beams would meet, forming an eight-shape, when the bomber would be at precisely the right altitude of 20 meters, and by a simple triangular aiming device of precise size, in which when held in front of the bombardier's eye, the two distant vertices would match the two towers on the dam wall when at the right distance for dropping the bomb.
The heavily loaded bombers flew very low all the way, along carefully planned routes, in order to minimize the risk of being hit by known anti-aircraft gun positions, or intercepted by night fighters, but once over the target, they could only attack a dam one bomber at a time, with delays between each, to let the water calm after each bomb's explosion. That gave the German anti-aircraft gunners, positioned on top of and near the dams, the opportunity to concentrate their fire at each incoming bomber while it was flying low and level over the dam's lake, heading right at them, and right in front of them.
Seven bombers did not make it to the dams. One bomber was lost from Gibson's formation on the way to the target. From the 2nd formation of five bombers, one was shot down by anti aircraft guns, one hit electricity pylons and crashed, one was hit by anti aircraft fire and lost both intercomm and radio, and therefore had to turn back, and one flew so low that its bomb hit the sea water and was torn off, so it had to turn back. So from the 2nd formation, a single bomber flew on, alone, to attack the Sorpe dam. And from the 3rd formation, the reserve, two bombers were lost on their way to the dams. The very low flying was essential, but so costly.
Charging forward in the face of the enemy, which does its best to kill you, requires great courage. Doing it again, and then again, requires the highest valour, as Gibson did next. After the 2nd bomber was shot down, Gibson ordered the 3rd crew to attack, and told them that he will fly his bomber over the dam again, in order to attract the enemy gunners fire at him instead of at them. Gibson's support helped. The anti aircraft gunners fired at him first, and noticed the lower attacking bomber too late. The bomber was hit, but kept flying. Its bomb hit the dam, which kept standing. The two bombers then supported the 4th bomber's bomb run, flying over it from both sides, firing at the enemy anti aircraft guns and attracting their fire at them. The huge dam was hit again, and still held.
When the 5th bomber made its bomb run, the two bombers flew over its two sides and this time also lit their navigation lights, to further mislead the enemy gunners and attract their fire from the attacking bomber. The huge dam was hit again, the 4th time, and then it was breached, massively, and well over 100 million tons of water started to massively flood the Mohne valley past the breached dam.
Gibson ordered two of the 'empty' bombers to fly home, and led the remaining five bombers, with three remaining bombs, to their second target, the Eder dam.
The single bomber which remained from the 2nd formation reached the Sorpe dam alone, faced similar topographic difficulties as in the Eder, and also increasing fog. After nearly crashing, it successfully dropped its bomb at the 4th attempt, but the Sorpe dam remained standing.
The reserve formation was then ordered by radio to fly to the Sorpe and attack it. Two bombers were lost on the way to the target. One bomber reached the Sorpe dam, which was already covered with fog, and at their 10th attempt, after setting the nearby forest ablaze, and still unable to see the dam itself, they made a successful bomb run and hit the Sorpe, which remained standing. Another reserve bomber then reached the Sorpe dam, but then the entire valley was covered with fog, so it flew back home. The last reserve bomber attacked a smaller dam, also in fog, and at its 3rd attempt was able to make a successful bomb run, and hit the dam, which remained standing.
One of the bombers returning from attacking the Eder was hit by anti aircraft fire over the Dutch coast and crashed to the sea.
Of the 19 heavy bombers which took off for the Dambusters raid, 8 were lost, a terrible loss rate. 53 crew members were killed, and 3 survived and became prisoners of war. The heroic courage, determination, flying skill, and sacrifice, of these brave airmen of RAF squadron 617, are almost beyond words. The Dambusters raid was a great success. Two huge dams were breached, causing tremendous damages to the Nazi war effort, both immediate and longer term damages.
After that, it was decided that the squadron would continue so serve as a specialized elite squadron for performing strategic attacks with very large bombs, but no longer in the extremely dangerous low flying attack profile. Squadron 617 then used Barnes Wallis' new "earthquake bombs", mainly the 12,000 lb "Tallboy" bomb, and in the last weeks of World War 2 they received, and used, the 22,000 lb "Grand Slam" bomb. The squadron used the most advanced bombing sights for these huge bombs, and also developed its own special target finding and marking method, which required great courage and skill from the pilot of the target marking aircraft, who was typically the squadron's commander. In that role, dropping the heaviest bombs with the highest accuracy, squadron 617 destroyed many German strategic targets until the end of the war, including V-1 and V-2 missile sites, massively fortified submarine pens, massive strategic bridges, rail tunnels, underground facilities, and the battleships Tirpitz and Lutzow.
World War 2 Bombers