After France fell, the British government was certain that Germany’s next move would be against the United Kingdom. These fears were confirmed when British intelligence intercepted coded German radio transmissions that made it clear that an invasion of Britain was imminent. Preparations in Britain had long been under way, and aircraft, guns, and ammunition were arriving by ship from the United States on a regular basis, despite the constant threat of attack by German submarines. The British would rely upon air and naval power as their primary defense, as they knew that they would quickly lose the war if German troops set foot on British soil in large numbers.
As Britain braced itself, one of its immediate goals was to prevent the French navy from falling into German hands. As a result, Operation Catapult was put into action on July 3, 1940. A British naval force based in Gibraltar was ordered to Mers-el-Kebir, Algeria, where much of the remaining French navy had fled. The British offered the French crews a choice: they could sail immediately for Britain and join in the fight against Germany, hand their ships over to the British, allow the British to move the ships somewhere safe in the West Indies, or scuttle their fleet. The French crews refused all four options, leaving the British little choice but to fire upon their allies, destroying the ships and killing over 1,200 French sailors. French ships at several other locations, however, were seized without incident.
The German code name for its plan to conquer the United Kingdom was Operation Sea Lion. The operation began tentatively, as a series of probing bomber attacks against British ships in the English Channel and ports in southern England in early July 1940. In fact, Hitler was still debating whether to invade Britain or Russia first.
The first German bomber attack over the Channel came on July 10, 1940. Yet even as late as July 19, Hitler made a last-minute speech advocating peace with Britain, presumably trying to buy time. Britain ignored the appeal. Skirmishes over the Channel and coastal southern England continued into August, but the Royal Air Force only rarely came out to defend the ships in the channel, preferring to hold off until the German planes got closer to the mainland, nearer to the limit of their range. As a result, British shipping in the Channel suffered heavy damage, but the RAF was able to conserve pilots and planes for the coming battle.
In early August 1940, Hitler decided to begin massive bombing raids on air bases and military command posts in southern England, hoping to break Britain’s will. Germany would withhold any attempt at a ground invasion, however, until it was clear that air superiority could be gained over England. On August 13, which the German high command labeled “Eagle Day,” Germany sent more than 1,400 bombers and fighters across the English Channel. The Germans brought down only thirteen British fighters that day but lost more than three times as many of their own aircraft.
Over the next several days, the Germans continued to suffer comparatively heavy losses. While this gave British pilots a certain sense of optimism, the sheer numbers of planes the Germans sent meant that many bombers were still reaching their targets. Nevertheless, even after three weeks of incessant attacks, the RAF was still very much intact.