a means of retaliation against illegal German minelaying. (Sir Edward Spears claimed that he had originally proposed the idea to Churchill, when they visited eastern France in August 1939 but by the time the operation began, Churchill believed the idea to be his.) A stock of mines, with 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. The sailors were to be based in the Maginot Line, about distant from the Rhine, to put mines in the river, interfering with commercial traffic for beyond Karlsruhe. The mines would sabotage barge traffic and other river craft but become inert before reaching neutral territory at the Netherlands border. On 6 March 1940, the Cabinet was notified that mines would be ready for release from riverbanks on 12 March and to be dropped by RAF bombers by mid-April, between Bingen am Rhein and Koblenz on moonlit nights. Neutrals were to be warned and the first mines were ready by the night of after French objections for fear of German retaliation, the plan was postponed. In April, Churchill tried to persuade the French to drop their objections to Royal Marine and remarked after meeting the French Prime Minister, Édouard Daladier, "". Mines The mines were specially developed for the operation by Ministry of Defence 1 (MD1, Churchill's Toyshop), a British weapon research and development organisation. The mine, known as the 'W' Bomb, was designed by Millis Jefferis, who had received the request for the device on 10 November and had completed the first demonstration model by 24 November. 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. Each mine contained of Trinitrotoluene (TNT). Trials of the mines were carried out in the Thames in December 1939 and depending upon type, either floated or bounced along the riverbed. 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. Over 20,000 'W' Bombs were produced in the course of the war. Operation On 10 May 1940, mines were released into the Moselle to destroy pontoon bridges built by