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Operation Chastise

The Air Ministry originally considered the Ruhr dams as a possible target as early as 1937. A number of proposals and studies were undertaken but none produced a proper plan, viable weapon or feasible means of delivery.


he aircraſt used on the Dambuster Raid of 1943 were modified Avro Lancaster B Mk III Special. Te weapon

was codenamed Upkeep and was the brainchild of Barnes Wallis of Vickers Armstrong, who had been working separately on some method of attacking dams but probably didn’t conceive of the bouncing bomb idea until Mar 42. He was given access to and assistance by a number of research bodies. Experiments involved exploding charges against model dams and the destruction of a 180 foot disused dam in Wales, giving Wallis valuable data, but it also showed that the task was far from easy and that any explosion preferably needed to take place in contact with the dam wall. Wallis persisted and meanwhile attempted to persuade the powers that be of the project’s viability in the face of bureaucratic hurdles and military scepticism.

Final approval came on 26 Feb 43. However, because the optimum time to attack was in the spring, when the reservoirs were full, it left little time. At the end of Feb 43 there were neither modified aircraft nor weapons, nor drawings of either.

With such short timescales, the firms involved, some of them natural rivals, had to co-operate or the project would be dead

22 Envoy Spring 2013

in the water. Under the direction of the Chief Designer, Roy Chadwick, Avros set to work on modifying the Lancasters, whilst Vickers-Armstrong made the mine casings and small drive engine for spinning the bombs. The Royal Ordnance Factory would fill the casings with the torpex explosive. The Oxley Engineering company provided the steel and the Hoffman Manufacturing company made the bearings for the drive mechanism. All these components and modifications had to be designed, manufactured and delivered in eighty days. The last modified Lancasters were delivered just three days before the raid.

After initial trials dropping scaled down prototype weapons from a Wellington at Chesil Beach, modified Lancasters were used to fly a series of tests dropping inert Upkeeps on the Kent coast. Mines were dropped at varying height and speed and differing bomb rotation speeds, while Wallis attempted to work out the optimum approach height and speed for the raid. He also had to establish that spinning a massive four ton cylinder at several hundred rpm would neither rip it from the calliper arms, nor seriously affect the aircraft’s flying characteristics.

On 21 Apr 43 Wallis decided to dispense with the wooden casing and run Upkeep as a bare cylinder. Three days later Wallis asked Gibson if he could drop the mine at 60’ and 232 miles per hour. At this speed

and if it was dropped at the right distance, the mine would survive the impact with the water, the aircraft would be clear of the splash, the weapon would carry all the way to the dam, and the aircraft would be flying fast enough to have some chance of getting through the defences.

A new squadron was formed at Scampton on 21 Mar 43, initially known as ‘X’ Sqn and latterly as 617 Sqn, and the 24 year old Wg Cdr Guy Gibson was personally selected to lead it by Air Chief Marshal Sir Arthur ‘Bomber’ Harris, the Commander-in-Chief of Bomber Command. Gibson was already the holder of four gallantry awards – the Distinguished Service Order and bar and the Distinguished Flying Cross and bar.

Despite the ‘elite’ tag and the presence of some very experienced airmen, not all 617 Sqn aircrew were veterans. Some had flown fewer than 10 missions and some of the flight engineers on the raid were flying their first operational sortie. Not all had volunteered and not all were known to or selected by Gibson: one entire flight of 57 Sqn was simply posted en masse to 617 Sqn.

The crews, who had trained to operate their bombers at heights above 15000’, with a measured approach to the target allowing accurate navigation, were put through intensive training to fly at night, at 150’ over water. Night-flying at that height with

Attack on Ruhr dams by aircraft of 617 Sqn on the night of 16-17 May 1943

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