Did the British really employ magicians and practical jokers?

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Extracts from memorandum by the First Lord of the Admiralty to the War cabinet, October 1941

Catalogue ref: CAB 86/1

Source a

Coal Dust Films for Camouflage of Coastlines

Memorandum by the First Lord of the Admiralty.

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In Battle of the Atlantic, S/50/79, Second Meeting, Conclusion 1, the Admiralty, in conjunction [together] with the Ministry of Home Security, were directed to experiment with the camouflage of tidal water by the application [using] of coal dust.

2. The appendix attached summarizes the results which have been carried out.

3. If the process is to be applied on the large scale required for the camouflage of major waterways or commercial port areas, the number of craft (boats) and personnel would, be very large, and the quantity of coal which would have to be transported would be prohibitive [make it not worth while]. For example to cover the Mersey alone, and outside the docks, would require a monthly consumption of 200,000 tons of coal, and the employment of at least 400 mobile units. This consumption is based on 10 moonlight nights of 10 hours each.

4. The coal will have to go somewhere once it is has been placed on the water. Some will be carried away by the tide, some will sink, and a little may remain temporarily suspended. The quantities involved will represent considerable siltage in rivers and estuaries which have already to be continually dredged to keep them clear.

6. In view of the large numbers of craft and personnel, and the great quantities of material, required, it seems doubtful whether this method will be a practical proposition.