Impact Facility SC

Impact Facility and WE177 Weapon

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Background

The Impact Facility was a structure built by AWRE Aldermaston on Orford Ness to test the ability of the WE177 series of low-level, free-fall, nuclear weapons to correctly detonate after experiencing any mechanical shocks incurred during a ‘Laydown’ landing.

 

The UK’s early atomic bombs, Blue Danube (24ft long/weighing 10,000lb), and Red Beard (12ft long/2,000lb), were large and cumbersome, required delivery by strategic bombers, and had operational shortcomings. With increased nuclear yields it became possible to produce smaller weapons that could be delivered from low-flying ‘tactical’ aircraft.

 

For the protection of the pilot and aircraft it became necessary to develop strategies to create a distance between the pilot and the location and timing of the detonation. This strategy was achieved in several ways including ‘Laydown’ bombing which was essentially a free fall, but parachute-retarded, landing - followed by a defined time-delayed ground detonation

The Impact Facility (or Hard Target

The Impact Facility on Orford Ness was build in 1963, operated until 1968, and consisted of three structures. These were (a) the ’Hard Target’ (a massive concrete wall and associated concrete apron and supported rail tracks), (b) a wooden Camera Gantry and (c) a shared Control Room.

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© Crown Copyright / AWE 2021 Contains public sector information licensed under the Open Government Licence v3.0.

To simulate the impact forces that a WE177 might experience during a ‘laydown’ delivery - when the weapon would strike the target with a low angle of attack - the weapon was fired into the concrete wall (hard target). This was done to assess the adequacy of the structural strength and the ability of its inbuilt timers (fuses) to reliably detonate with a pre-determined delay after a landing impact. Its fissile component was not present, but often its high-explosive components were.

 

A WE177 was mounted on a rocket-propelled wooden sled that travelled along a rail track to impact the wall at 150mph. Impact data, transferred via an umbilical cord from sensors within the weapon, was recorded externally. The impact was also recorded on Vinten high speed film cameras mounted on a wooden gantry some 50ft above the impact point.

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WE177 after 1965 Impact Trial

© Crown Copyright / AWE 2021 Contains public sector information licensed under the Open Government Licence v3.0.

Some WE177 impact trials involved changing the temperature of the warhead and its high explosive components, between +100 C and -40 C. In other trials weapons were subject to combined vibration and temperature stress testing: these were carried out in one of two local  'Pagoda' test cells

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The WE177 series

The WE177 was Britain’s last free-fall nuclear weapon and was in use between 1966 and 1998. It was produced with three different variants for different targets and had a wide range of selectable nuclear yields. Versions A and B were both high-yield ‘strategic’ weapons, but C was a low-yield ‘tactical’ weapon. A and B were in service with the RAF from 1966 and C, used as a ‘depth bomb’ by the Royal Navy, from 1971. Weapon delivery could be from a wide variety of aircraft including Britain’s V-bombers (Valiant, Victor and Vulcan), tactical aircraft (such as the Canberra and Buccaneer) and helicopters (such as the Wessex and Lynx). For a very comprehensive report on the evolution and history of the WE177 itself see the report by Dr John B Walker. 

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Impact Facility - 2018 Photograph

This shows the condition of the Impact Facility some 50 years after its closure .This is typical of most of the other cold war structures on Orford Ness.

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Further information can be found in the full report and further images and videos are available via the Drawings, Photographs and Graphics buttons, above.