The Flixborough Explosion
The Flixborough disaster was an explosion at a chemical plant close to the village of Flixborough, North Lincolnshire, England on Saturday, 1 June 1974. The massive shockwave and resulting disturbance to the earth's Ionosphere was picked up by the experimental radio equipment at RAF Blakehill which was by then being used by GCHQ. This disaster led to the MOD's interest in the impact of disruption to radio transmissions should a nuclear attack be launched on the UK. My thanks to Dave Ineson for sending me the highly complex background documentation written by academics of the time who were involved in the research that followed.
This is an image of the trace picked up by Blakehill's equipment and the triangulation diagram showing the location.