Operation “Sea Lion” – Invading England In 1940? [Part One]

November 7, 2016 by crew

Good day, Beasts of War. Oriskany here, back from my “Sci-Fi vacation” and ready to once more plunge into the dusty labyrinth of historical wargaming. For the topic of this next article series, I thought we could explore one of the most fascinating and debated invasions of World War II that never happened: Operation Sea Lion.


Put broadly, Operation Sea Lion (Unternehmen Seelöwe in German) was Germany’s plan to invade Great Britain in the summer or fall of 1940. After the spectacular success of “Case Yellow” and “Case Red” (the two-phased invasion of the Belgium, Holland, Luxembourg, and France), invading the UK seemed the next logical step. Or was it?

As we’ll explore in this series, the German war machine faced a staggering array of obstacles just to contemplate such an operation. However, they also enjoyed a wide range of very comfortable advantages. We all know it never happened. But could it have? Really? And if it had, what would it have looked like?

This series will look at the plans, conditions, and “best guesses” at some of Sea Lion’s possible outcomes. We’ll also feature a campaign-style series of wargames, featuring systems like Battlegroup (Ironfist Publishing) and Panzer Leader (Avalon Hill). Win, lose, or draw, we are GOING to invade England, and see what happens on the tabletop.


We’ll break Operation Sea Lion down in five articles. Article One will introduce the project and review some of the actual plans the OKW (Oberkommando der Wehrmacht) was looking at. The obstacles and advantages on both sides will be discussed, along with the preconditions the Germans would have to meet before Sea Lion could be launched.

Article Two will feature the assault and lodgement on the coasts of Sussex and Kent. Article Three will see the Germans expand their bridgehead, and Article Four will bring our imagined campaign to a climax. Finally, Article Five will make the case for Sea Lion, and offer a considered opinion on whether this really could have happened.

Sea Lion: The Prospects

Here on Beasts of War, we all love our alternate history. Yet while it’s chilling to imagine a swastika flying from Big Ben, or Winston Churchill and King George VI sharing a cell in the Tower of London, it’s important to take a hard look at the cold, hard facts...and measure the actual conditions faced by both sides of this prospective campaign.


As we all know, Germany had just conquered France. The British Expeditionary Force (BEF) had just been hurled off the continent, having been forced to abandon just about anything heavier than a Bren gun. The Germans seemed unstoppable, and boasted that the English Channel “was just one more river to cross” to invade England.

This, of course, is absurd. The English Channel poses a much bigger obstacle to cross than any river, especially when defended by the largest navy in Europe. But was the Royal Navy really that strong? Most of their ships were far past their prime, and spread over the globe to protect the sea routes that kept Great Britain alive.

But if the Royal Navy wasn’t as strong as it appeared, neither was the German Army. Despite most misconceptions, the invasion of France had been no walkover. The Germans had lost tens of thousands of men, tanks, and aircraft, and most formations in the summer of 1940 were now badly understrength and in need of rest.


The Germans also had no unified command structure, critical in a sea-air-land operation like Sea Lion. Nominally, the OKW had authority over the Wehrmacht (Army), Kriegsmarine (Navy), and Luftwaffe (Air Force), but in practice cooperation was poor and inter-service rivalries would plague the German war effort throughout World War II.

Then again, the German invasion of Crete in May, 1941 shows that the Germans could follow up a mainland European invasion by quickly bounding over hostile waters controlled by enemy naval units, establish a bridgehead on a defended island, and then expand the bridgehead to secure the island.

Of course, Great Britain is not Crete. Still, it teases the imagination with what just MIGHT have been possible, at least in the early stages of Sea Lion. In any event, our fifth article will take a much more detailed “pro and con” evaluation of Sea Lion’s prospects.

Sea Lion: The Plans

Another misconception many people have about Sea Lion is that there was ever “a” plan. There were several plans, perhaps half a dozen or more. All were very different and covered a wide array of potential invasion scenarios.


For purposes of brevity, these plans fall into two basic categories: those proposed and favoured by the Kriegsmarine and Luftwaffe, and those proposed and favoured by the Wehrmacht.

In summary, the Navy / Air Force plan called for a very narrow invasion corridor, with one assault zone extending from Hastings to Rye in the west, and a second from New Romney to Folkestone in the east. A lead proponent of this plan (drawn up as early as November, 1939) was Grand Admiral Raeder, commander of the Kriegsmarine.

Clearly, the Kriegsmarine and Luftwaffe wanted a narrow invasion corridor because this would be much easier for them to establish over the English Channel, protect against RAF and Royal Navy interference, and maintain a reasonable flow of supplies once a beachhead was established.


The Wehrmacht, however, hated this idea. To launch an invasion on such a narrow, vulnerable front (with only four initial divisions in two corps) seemed in their eyes nigh-suicidal. They wanted a much wider invasion corridor, with some plans calling for landings as far west as Portsmouth, Southampton or even Weymouth.

Of course, both plans were unrealistic. The Kriegsmarine and Luftwaffe could never hold open the Army’s overly-ambitious proposed invasion corridor, nor could the Army spearhead an invasion of England with just four initial divisions on such a narrow front.


On July 16th, 1940, Hitler issued Direction No. 16, his order to begin preparations for invasion. The German Army, Navy, and Air Force now had to come up with a workable compromise plan, finalized on or about August 30. Since these are the most plausible and well-documented, we’ll use these plans as a basis for our exploratory campaign.

Sea Lion: Prerequisites

The most immediate and incontrovertible prerequisite for any realistic contemplation of Sea Lion is of course that the British have to decisively lose the Battle of Britain, the gigantic, months-long air battle to control the skies over England. Starting in July, 1940, the British historically won the battle, Germany’s first real defeat of World War II.

For the Germans to have any chance at all, we have to imagine they win this battle, and win it badly. Such a result is possible, looking at German operations starting on “Adlertag” (Eagle Day - August 13th), a concerted effort to destroy RAF airfields and other vital infrastructure and force RAF fighters into combat against superior numbers.

This endeavour started very well, and within weeks the RAF was almost dead on its feet. Only when Hitler and Göring make the spectacular mistake of switching emphasis to attacks on British cities does the RAF get the reprieve it so desperately needed to recover.


So if we imagine the RAF largely crippled by early September, 1940, we now face other conditions the Germans have to meet. The first is a shipping fleet to get their troops across the Channel. In this, they were surprisingly successful, largely by appropriating thousands of small craft from the many ports of Holland, Belgium, and northern France.

The Germans also had specialized equipment ready to go, including four full battalions of “tauchpanzer” submersible tanks, based on the PzKpfw III. The Germans also had their ace in the hole, the best airborne assault force in the world, including gliders, an airmobile division, and of course the dreaded “Fallschirmjäger” parachute troops.

These specialists are the real key to initial success for Sea Lion. The German vision for Sea Lion was much less a “Saving Private Reinhardt” scenario with troops hitting a fortified, defended beach. Rather, airborne troops would take airfields, ports, and even beaches, on which heavier German seaborne formations could land in relative peace.

The other critical condition facing the Germans was time. Fragile as it was, any prospect for Sea Lion would have to be carried off before the middle of October at the latest. The weather over the English Channel tends to get borderline apocalyptic at that time, especially for any army trying to mount an assault across it.


The Germans also had to hurry before the British were able to recover too much from their defeat in France. While many men had escaped at Dunkirk, there was practically nothing in the way of heavy artillery, tanks, or other equipment. But the British were recovering fast (with the help of the Americans), so time was short.

Sea Lion: Getting Started

Of course, this is only the start of what I’m sure is a fascinating, controversial, and provocative topic. While certainly full of charged opinion, simply asking “would Sea Lion have worked” is a blatantly oversimplified question. We’re just exploring what might have happened if the Germans tried it, the prognosis will be presented in Part Five.

Also, the plan will be covered in more detail as we game through the opening battles. Again, we’re using the “compromise” plan widely published, others will certainly have opinions, ideas, and quotable sources on other plans. Please remember there were many plans and we’re just using the most plausible and well-documented one.

For now, let’s just sit back and imagine that just maybe, somehow . . . the Luftwaffe has managed a victory in the Battle of Britain. There was never a “Blitz” against British cities, the Germans just kept hitting the RAF where it could really be hurt, at its bases on the ground. Now, the RAF is all but gone, and the Germans own the air.


Now, the skies over Sussex and Kent are dark with German Heinkels, Dorniers, and Stukas. Huge 15-inch guns are installed at coastal batteries at Calais and Boulogne, ready to hurl 1800-pound shells across the Channel at targets from Folkestone to Hastings. The U-boats pull back from the Atlantic and now nest thick in the English Channel.

The date is September 15th, 1940. Across a darkened, blacked-out England, the roar of German bombers is replaced by the drone of hundreds of Ju-52 transport planes, some loaded with paratroopers, others towing DFS-230 gliders.

The die is cast. Operation Sea Lion is about to begin.

By James Johnson

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"Win, lose, or draw, we are GOING to invade England, and see what happens on the tabletop..."

"The most immediate and incontrovertible prerequisite for any realistic contemplation of Sea Lion is of course that the British have to decisively lose the Battle of Britain..."

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