Three pens were arranged in a curve. One has been completely removed. Of the two remaining; the unique example survives that was used to test all ‘jump jets’ or VTOL. The VTOL pen is lined with metal sheeting and sound absorption. Historical significance is for the development of the ‘jump jet’, P1127 through to the Harrier.

Three engine running or detuning pens were originally built in the early 1950’s to test the aircraft engines for the Hunter prior to delivery. By 1960 the Eastern-most of the three pens was modified specifically for engine testing of the P.1127 and later the Harrier. This pen was modified and excavated to form a void which was fitted with a blast grid to diffuse vertical thrust. At the rear of the pen, a new diffuser was fitted to contain thrust when the engines were vectored to the rear. At the same time, a second control room was added and the inside of the pen was fitted out with metal covered insulation. A double-depth metal sliding door was also installed at the entrance so that when closed, noise and debris were suppressed.

As CTP Bill Bedford recounted, in 1960 when undertaking the first testing of the engine for the prototype P.1127 there was an engine fire. The “elephant ears” noise baffles either side of the aircraft had to be rapidly moved out of the way to allow fire crew to access the exhaust to dowse the fire.

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