Operation Sledgehammer was an Allied plan for a cross-Channel invasion of Europe during World War II, as the first step in helping to reduce pressure on the Soviet Red Army by establishing a Second Front. It was to be executed in 1942 and acted as a contingency alternative to Operation Roundup, the original Allied plan for the invasion of Europe in 1943. Allied forces were to seize the French Atlantic ports of either Brest or Cherbourg and areas of the Cotentin Peninsula during the early autumn of 1942, and amass troops for a breakout in the spring of 1943.
The operation was eagerly pressed for by both the United States military and the Soviet Union, but rejected by the British, who concluded a landing in France was premature, and hence impractical. As a result, Sledgehammer was never carried out, and instead the British proposal for an invasion of French North Africa took place in November 1942 under the code name Operation Torch.