Part of the plan was for Royal Air Force (RAF) bombers to drop the mines into rivers and canals on moonlit nights but this had hardly begun when the campaign ended.

[1] Wilfred was to force German convoys transporting Swedish iron ore into international waters, where they could be attacked by the Royal Navy.

)[7] A stock of 2,000 fluvial mines, with 1,000 more being produced per week, were to be put into rivers in France that flowed into western Germany, by naval parties led by Commander G. R. S. Wellby.

Neutrals were to be warned and the first 300–400 fluvial mines were ready by the night of 14/15 March; after French objections for fear of German retaliation, the plan was postponed.

A delayed-action fuze based on a soluble chemical pellet was devised by Jefferis' assistant, Stuart Macrae, using an Alka-Seltzer tablet, which was found to dissolve at a predictable rate.

[11] Because Jefferis' department only consisted of three people at the point, the trials had to be conducted with the help of a boat crewed by local Sea Scouts, who followed the mines after they had been dropped from Chiswick Bridge.

[14] On 13 May, the British put 1,700 mines in the Rhine near Soufflenheim, reported by General Victor Bourret, the Fifth Army commander, to have caused damage to the barge barrier protecting the bridge at Karlsruhe.