By late March 1940, the plan to mine the Norwegian waters, which Churchill had been urging his colleagues to authorise but for a variety of reasons had still not been carried out, had become linked with a separate plan to send naval mines down the Rhine to destroy German pontoon bridges, barges and shipping further downstream. The latter plan, known as Operation Royal Marine, was seen by the British as a way of striking back for the heavy damage and loss of life the Germans had inflicted on them by the use of the magnetic mine, but the French vetoed the plan for fear that it would bring a wider German retaliation against them.[1]