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For individuals in countries that have escaped military invasion and occupation, imagining what such an ordeal would have been like can be a popular pastime. In the 1970s, armchair generals could play “Invasion: America,” a board game in which the fictional European Socialist coalition, South American Union, and Pan Asiatic League try to overrun the United States and Canada. In 1984, American audiences flocked to theaters to watch Red Dawn, a film about doughty high school kids who wage guerrilla war against the Soviet bloc forces that had invaded the western United States. The 1987 television miniseries Amerika depicted a far-from doughty United States accepting Warsaw Pact domination after a bloodless takeover.

The British, too, have often imagined what a foreign invasion would be like. Such musings have included It Happened Here, a 1966 movie portraying a German occupation primarily enforced by the Nazi sympathizing British Union of Fascists; Hitler’s Britain (2002), which depicted the roundup of Jews and Socialists and the crushing of a British guerrilla uprising; and Island at War (2005), a five-part Masterpiece Theatre production dramatizing the plight of British residents after the actual German occupation of the Channel Islands in 1940. But the most elaborate efforts lie in a number of counterfactual histories detailing a successful execution of Operation Sealion, as the Germans called their plan for an invasion of southern England. Of these, the most noteworthy is military historian Kenneth Macksey’s Invasion: The Alternate History of the German Invasion of England, July 1940, published in 1980 and still in print after three decades.

Macksey’s point of departure is the fact that in July 1940, the British armed forces were at their weakest. Following the evacuation of Dunkirk in late May and early June, the British army, forced to leave behind nearly all its heavy equipment, was left with only a few hundred usable tanks. The Royal Air Force had also taken a beating and was still rebuilding itself. The British had few beach defenses in place and their proposed main line of defense, the GHQ (or General Headquarters) Line, existed only on paper.

The window of opportunity this created for the Germans was narrow, however. Macksey believes that it would have diminished substantially by August and disappeared altogether in September. The only reasonable chance for a successful German invasion lay at the Strait of Dover, where the English Channel is only about 20 miles across. Here alone the Germans could fend off the Royal Navy, thanks to a combination of warships, shore-based heavy artillery, a massive air umbrella, and minefields at either approach to the strait.

Macksey’s rewrite of history begins on May 21, when Grand Admiral Erich Raeder approached Hitler about the prospect of invading Great Britain. Hitler in actuality dismissed the idea and did not revisit it until the British failed to do as he anticipated: sue for peace after his conquest of France. But in Macksey’s account, the idea captivates the Nazi dictator. He throws the weight of his absolute power and unshakeable will behind plans for a cross-channel attack. A third of the German army in France is set aside to participate.

The aerial Battle of Britain begins slightly earlier than in reality, in June, and for the most part follows the course it took historically. Although it does not culminate in complete German success, the Germans nonetheless launch Operation Sealion on July 14. The invasion begins with a predawn airborne attack that isolates the meager British defenses between the coastal towns of Hythe and Dover, paving the way for a cross-channel assault. By day’s end the Germans are firmly ashore. A British counterattack, with their limited armored force, fails; the Germans expand their beachhead and then break out. By month’s end they have closed in on London and the British government agrees to make peace. The book closes with a puppet government ascending to power on August 2, 1940.

Macksey’s scenario for a cross-channel attack is highly plausible, and he plays fair with available facts and the difficulty of mounting such an operation. As he imagines Sealion, it is a near-run thing, based on historical data on the relative strength of British and German forces at the time. The main rewrite is that German preparations for the invasion begin sooner, are vigorously pursued, and the invasion itself is launched even though it remains a risky proposition.

The main weakness of Macksey’s scenario is that it assumes a prompt British collapse. The demands of a book-length alternate history require him to pursue the story to resolution, and a swift political collapse allows him to avoid one of the main pitfalls of counterfactual history: that of piling one speculation atop another. But a single shift in the historical narrative does not mean that one can predict a single outcome. The alternate world the initial shift creates would logically have “nodes of uncertainty,” critical points at which events could follow more than one path, from which the counterfactual analyst must select the most probable outcome. Even if each choice has a 90 percent probability of being correct, after 10 such choices the probability of arriving at any particular outcome is less than 1 percent.

Thus Macksey wisely, in one sense, keeps the nodes of uncertainty to a minimum. But this narrative strategy means that he cannot take seriously Winston Churchill’s eloquent insistence that the British would “defend our island whatever the cost may be; we shall fight on beaches, landing grounds, in fields, in streets and on the hills. We shall never surrender and even if, which I do not for the moment believe, this island or a large part of it were subjugated and starving, then our empire beyond the seas, armed and guarded by the British Fleet, will carry on the struggle until in God’s good time the New World with all its power and might, sets forth to the liberation and rescue of the Old.”

As Stephen Budiansky makes clear elsewhere in this issue, the British had plans to conduct a guerrilla campaign even if conventional defense became impossible (see “Churchill’s Secret Army,” page 28). A scenario in which the British continue to resist greatly complicates the ability to predict a plausible ultimate outcome. The Germans might, for instance, have been pinned down in a protracted guerrilla campaign—as they were in Yugoslavia from April 1941 onward. If that occurred, it might have taken as many as a million troops to maintain a sure grip on Great Britain. (It took several hundred thousand troops just to garrison Norway.)

As a consequence, while a successful Operation Sealion would have better positioned Germany for an invasion of the Soviet Union, it would not necessarily have made victory over the Soviet Union inevitable. The specter of a Europe dominated by Hitler would, furthermore, surely have had implications for American foreign policy. And the vicious German occupation of a nation with which the United States possessed close ties almost certainly would have accomplished exactly what Churchill hoped, with the New World set ting forth to rescue the Old.


Originally published in the November 2008 issue of World War II Magazine. To subscribe, click here