Operation Royal Marine

Operation Royal Marine was a military operation in World War II, in which naval mines were floated down rivers from France into Germany to destroy bridges and shipping.

Promoted by Winston Churchill, it was planned in November 1939. However, 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 was put into practice Churchill believed the idea was his. Trials of the mines were carried out in the Thames in December 1939. Each mine contained 15 pounds (6.8 kilograms) of TNT and, depending upon type, either floated or bounced along the riverbed. The mines were especially developed for the operation by MD1.

Despite concerns by the French government during the Phoney War over possible German reprisals against French waterways, it was intended that the operation would take place simultaneously with Operation Wilfred, a scheme to mine the waters around Norway in order to force German convoys using them for transporting Swedish iron ore into international waters, where they could be attacked by the Royal Navy. Simultaneously attacking Germany with riverine mines was intended to deflect criticism that the Allies were not making war on Germany, only the small countries around it that they claimed to be protecting. However, a decision of the Anglo French Supreme War Council on 28 March 1940 to commence Operation Royal Marine on 4 April was vetoed shortly afterwards by the French government, leaving Operation Wilfred to take place on its own. In the event, Operation Wilfred was aborted shortly afterwards because of the German invasion of Norway.

Nevertheless, the river mining operation was carried out at the start of the Battle of France in May. During the first week of the battle, naval personnel under Commander Roger Wellby put 1,700 mines in the Rhine, resulting in the temporary suspension of most of the river traffic between Karlsruhe and Mainz and causing damage to the barrage at Karlsruhe and several pontoon bridges. By 24 May, over 2,300 mines had been released into the Rhine, Moselle and Meuse.

It was also planned that the Royal Air Force would drop mines into the Rhine between Bingen and Coblenz, into canals, and into river estuaries feeding the Heligoland Bight. Small quantities of mines were laid by aircraft during the closing stages of the battle.