The new squadron began training for the mission almost immediately. They had very little time to prepare. At this time they had yet to be given a squadron number (eventually it would be 617 Squadron) but initially they were known as Squadron X. Learning low flying both day and night was the first and most important task for the crews.
Upkeep test drop during training
Although it may seem unlikely for experienced air crews, air sickness was the first problem many of them had with low flying. Flying at low level caused intensive turbulent shaking of the aircraft and many of the crews who were used to operating at the rather smoother altitude of 10,000 feet experienced it. Medicine was handed out to those who needed it but some had to be rejected and replaced.
The flying was very intensive; night after night they practiced at first in borrowed Lancasters and later in the modified types as they came through from Avro. In order to make conditions as realistic as possible, they were told to fly over three main locations in England. The Eyebrook reservoir at Uppingham in Leicestershire, the Abberton reservoir near Colchester and the Derwent reservoir near Sheffield. It is important to remember that neither Gibson nor the crews were aware of their targets at this time, the information was absolute top secret and very few people knew. The crews were however beginning to guess what their target may be. At first the rumours were that the target was the German battleship Tirpitz.
Although Gibson was not told officially the target, he was given a very good idea of what he was up against at a meeting with Wallis on March 24th 1943. This was the first time the two men had met. Wallis could not tell Gibson specific details of the mission as he was not on the list of people with clearance for a full briefing, he did however tell him as much as he could. After the meeting, Gibson left in the certain knowledge that his aircraft must attack the targets at a speed of 240mph at a height of 150 feet, any variation on this and the plans simply would not work.
On the same day, Squadron X was officially designated the number 617. They were now officially 617 Squadron.
At the end of April 1943, the squadron had flown over 1,000 hours in training and as expected they had encountered special problems with flying at low level and simulating night time flying. The main four problems were:
- Simulating night time flying in daylight.
- Following a map at low level.
- Maintaining a height of 150 feet.
- Estimating the release point of the weapon from the target to ensure an accurate impact.
The first two problems were relatively easily solved. In order to simulate night flying during the day, blue celluloid was fitted over the cockpit windscreen, side windows and gun turrets while the crew wore amber-tinted goggles. Map reading was made easier by producing strip maps on rollers following each aircraft's particular route.
Establishing Height: How the lamps work
Height was a much more difficult and crucial problem. Normal Main Force squadrons relied on numbers and mutual defence to confuse and overwhelm enemy radar and defences. However, a small group of bombers flying at normal operational height would soon be either; detected and destroyed by enemy fighters, or successive waves of anti-aircraft batteries from the coast to the target. Not only would the attack have to come at low level, the entire flight there and back would have to be done at low level too.
The problem was that the standard altimeter was useless at low levels such as 150 feet. On March 28th 1943 Gibson with Hopgood and Young on board, had flown over the Derwent reservoir to see how difficult it was to fly over water at 150 feet with hills all around. During the daylight he had no real problems but when dusk came he could not distinguish the horizon from the water surface and nearly flew into the lake.
The solution to flying at 150 feet was found by the Royal Aircraft Establishment. A year earlier they had been experimenting with spotlights fitted under Hudson bombers in order to gauge their height while attacking U-boats at night. It had not worked very well due to choppy waves in the sea but over a smooth lake it might. After experimenting with it for a while, two lamps were fitted, one in the nose and one behind the bomb bay. They were angled so that the two beams would meet when the aircraft was at exactly 150 feet. It would be the job of the navigator to look down through the starboard (right) cockpit window and talk the pilot down until the lamps met at the required altitude.
Both Harris and the crews of 617 squadron were very shocked at the idea of lighting up an aircraft at the moment it was about to attack when it was at its most vulnerable. Harris was furious "I will not have aircraft flying about with spotlights on in defended areas" he said angrily. Although he was right, there was no other way to achieve the required altitude. The bombers would have to attack lit up.
The problems the crews were having with training were slowly being solved and they were becoming good at flying to the limits specified for the attacks. The development of Upkeep was not coming along so smoothly though…
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