Lynmouth in Devon is widely known for its disastrous flood of August 15th, 1952. After several days of almost continuous thundery rain, the rivers of the East and West Lyn rose to alarming heights, filled to overflowing with waters from the large Exmoor catchment. In the 24 hours immediately preceding the disaster, 200 mm of rain were recorded at several spots in the vicinity.
Ultimately, a 12-foot wall of water descended on the hapless town. Large boulders and rocks were carried through the streets, destroying houses, roads and bridges, and forming a pile 20 feet high along the High Street. The search for bodies lasted several weeks, and 31 were found.
There were strange stories about the Lynmouth flood. In the days preceding the disaster small aircraft had been seen apparently spraying crops in the area. Then rumours arose that rain-making experiments had been carried out by government scientists, and that therefore the military authorities might have been responsible for the disaster. And in fact declassified documents released in 1997 duly confirmed that government aircraft had indeed been "seeding" clouds around that time.
The technique of cloud-seeding began in 1946 when it was found that if powdered carbon dioxide, or "dry ice", was dropped into a bank of cloud, it sometimes facilitated a fall of rain. The particles of dry ice, or the silver iodide also often used, act as a catalyst, encouraging the water droplets of a cloud to change into natural ice crystals, which in turn enhance a cloud's ability to produce rain.
At the time of the Lynmouth flood, the cold war was at its height. The British government's interest in rain-making allegedly stemmed from its ambition to develop techniques to flood enemy trenches in the event of a Soviet invasion. Mud resulting from rain produced to order could paralyse enemy forces on the ground, impede the progress of their tanks, and increase the water flow in rivers to prevent a crossing.
In practice, however, it turned out to be difficult to assess the efficacy of such a process. Rain might well occur after local clouds had received the seeding treatment - but who was to say that it might not have rained in any case, even without this human intervention?