The Sea Lion that sank

Operation Seelöwe

A landing raft consisting of several boats, created to transport a field howitzer during the invasion of Great Britain
(Photo: Bundesarchiv)

One of the evergreen hypothetical questions of World War II is “What if Germany invaded Britain?” War history buffs often ask the question, and, in fact, the Royal Military Academy at Sandhurst in Great Britain held a wargame (Read our earlier article) in 1974 to find their own answers. What they found, and what the overwhelming majority of historians also believe, is that the attempt would have ended up in a catastrophe for Germany. Today’s article is about Operation Sea Lion, the planned but never attempted invasion of the United Kingdom.
Nazi Germany invaded France in May 1940, and achieved clear victory in a month and a half. The British Expeditionary Force was forced to retreat and was evacuated at Dunkirk between May 25 and June 4.
(Read our earlier article) 338,000 soldiers made it to safety in Britain, though at the cost of having to abandon all heavy equipment. British morale was sagging after the months of the Phoney War when Britain and France were already at war with Germany but saw little action, and the sudden shock of the loss of France. The table seemed set for Germany’s next step: forcing Britain out of the war.

Soldiers on the Dunkirk beach being strafed and bombed by German aircraft
(Photo: Australian War Memorial)

Much speculation has been made about the German decision to stop their armor before they could attack the British forces trapped at Dunkirk. The order was requested by General Gerd von Rundstedt and granted by Hitler, but the motivation behind it remains unclear. Some historians argue that von Rundstedt requested the stop to let the units rest and resupply for perfectly valid tactical reasons; others suggest that Hitler was making a gesture of peace to Britain by allowing the men to escape. Once thing that’s sure is that Hitler was hoping to get the United Kingdom to surrender to terms without a fight – he was already eyeing the Soviet Union, and knew that every bit of resource spent on forcing Britain to its knees was resource unavailable in the east. Of course, what the Führer did not realize was that British public sentiment and Churchill’s intransigence on the matter made any sort of surrender impossible.

Churchill in 10 Downing Street during the war
(Photo: Imperial War Museums)

The idea of invading Britain had been floating around since September 1939, the beginning of World War II. Hitler’s Directive No. 6 called for an offensive to “win as much territory as possible in Holland, Belgium, and northern France to serve as a base for the successful prosecution of the air and sea war against England.” Grand Admiral Erich Raeder, commander-in-chief of the German navy, the Kriegsmarine, anticipated a possible invasion of the island nation and had his operations officer draw up a document about the possibility of such an action. The paper identified four prerequisites for such an invasion to have a chance of success: destroying the Royal Navy or keeping it away, destroying the Royal Air Force (RAF), destroying all Royal Navy units in the landing zones, and preventing British submarines from interfering with the landings.
The Heer, the German army, wrote its own study paper in December 1939 with input from both the Kriegsmarine and the Luftwaffe. The study suggested an attack in Britain’s eastern coast with 100,000 men; the navy would simultaneously transport these people and keep the Royal Navy away from the operation, while the air force would control the air over the landing zones. Both the navy and air force rejected the idea. The former pointed out that it had no chance of standing up against the Royal Navy’s Home Fleet, and that organizing transportation for that many men would take a year; Luftwaffe-chief Hermann Göring declared that a landing in Britain could only succeed if the country was already completely beaten.

Göring (second from left) visiting a Luftwaffe base during the Battle of Britain
(Photo: Bundesarchiv)
The idea of invading Britain if they refused to surrender was dusted off in the summer of 1940 during the fall of France.  Hitler was already turning his attention to the Soviet Union and wanted the matter of Britain to be settled before 1941. On July 2, 1940, German high command began preliminary planning on the invasion with the understanding that it could only go ahead if the Luftwaffe managed to neutralize the RAF first by destroying its aircraft and production facilities. On the same day, Grand Admiral Raeder visited Hitler and tried to persuade him to pressure Britain into surrender through a combined air and submarine siege. Hitler agreed that an amphibious invasion had to be the last resort if all other attempts failed.
Grand Admiral Erich Raeder with Hitler in 1943
(Photo: Bundesarchiv)

The first version of the invasion plan was called Löwe, “lion,” and described as “a river crossing on a wide front,” which greatly irritated the Kriegsmarine, which was the only arm of the German military with an inkling of just how difficult the naval part of the operation would be. The name was later expanded to Seelöwe, literally “Sea Lion” (a relative of seals). While Germany went to some effort to disguise the nature of upcoming military operations in their names, this particular choice of name was not very clever. The idea that Operation Sea Lion might be a naval operation against a country whose coat of arms prominently features lions was not a difficult leap. In fact, British intelligence deduced the general nature of the operation from the name alone.

A German halftrack being unloaded during an exercise
(Photo: Bundesarchiv)

Unlike the 1939 army study, Sea Lion called for landing along the southern coast of Great Britain. More specifically, it first called for an extremely wide front stretching from Ramsgate in the southeast corner of the island to Lyme Bay to the west of the Isle of Wight – the front would have been more than three times wider than the one established by the Normandy landings on D-Day. The plan originally called for over forty divisions to land on the British coast in three waves. The first wave would mainly comprise infantry and some flamethrower tanks; the second would be bulk of the tank forces and the motorized infantry; the third wave would bring more footsoldiers. The first wave would also land thousands of horses to pull heavy equipment once the advance inland began. Two airborne divisions would land behind enemy lines, though the army and the air force could not agree on whether this should happen simultaneously with the first landings or afterward.

Map of the “broad front” version of Operation Sea Lion
(Image: Wereon / Wikipedia)
The army wanted the landings to occur at daybreak; the navy wanted them to take place two hours after high tide and under half-moon light so the unwieldy landing craft wouldn’t keep crashing into each other. These considerations greatly limited the possible dates for the invasion. A beginning date of September 15 was considered in late August and later revised to September 21. After that, however, autumn fog and rain over Britain and the English Channel would have hindered the Luftwaffe, limiting its ability to contribute.
The Luftwaffe was responsible for eliminating the RAF; in fact, the Battle of Britain had already begun on July 10, 1941, six days before Hitler issued a directly openly calling for Seelöwe. The main points of preparation were the removal of British naval mines at the crossing points, deploying heavy artillery to the coast to dominate the English Channel, and keeping the Royal Navy too busy in the Mediterranean and the North Sea for them to interfere with the landings. The plan’s success largely rested on Raeder’s and Göring’s shoulders, and both of them hated that fact. To make things worse, Hitler did not make provisions to establish a combined headquarters for joint planning (the Supreme Headquarters Allied Expeditionary Force would be such an organization years later), allowing the various branches of the military to try and push responsibility on the others.
Hermann Göring and Erich Raeder in early 1940
(Photo: Bundesarchiv)
The plan had several massive problems, the most obvious being that the navy did not have the transport ships to ferry the invasion force to Britain. While the D-Day landings relied on landing craft designed specifically for the job, such as the Higgins boat (Read our earlier article), Germany had to make do with whatever already existing vessel it could scrounge up. In the two months they had, they gathered 2,400 civilian river barges (two-thirds of which did not have an engine), tugs to pull the barges (including the powered ones which didn’t work well on the open sea), small motor launches and coasters (cargo ships designed for use in coastal areas).  The barges then had to be modified to make them minimally seaworthy and also give them a front ramp so troops and vehicles could disembark. The Luftwaffe offered to outfit some of the unpowered barges with a pair of aircraft engines and propellers that would act as makeshift ship’s screws. The Kriegsmarine was highly skeptical of the idea but the army accepted it enthusiastically, eventually receiving a complement of barges that couldn’t move backwards, had poor maneuverability, and were so loud that communication by shouting was impossible onboard.
River barges gathered for the planned invasion
(Photo: Bundesarchiv)
2,400 barges might sound like a lot, but it wasn’t nearly enough for the grandiose 40-division landing plan across an extremely wide front. Unpowered barges were supposed to run aground at high tide in the morning, then sit there all day until they could be retrieved during the evening high tide. They would then need to be towed back to France for repairs and more soldiers, make the crossing again, and start all over. The first wave itself comprised three separate echelons, and there were just not enough transport ships to ferry everyone and everything across in one go. The first wave alone would have taken four days to make landfall at different locations, and it would have taken another ten days or so for the heavy equipment of the second wave to be loaded onto the boats in France and sent across the Channel. In that time, the first wave would have had to hold positions, or even try to occupy ports, with whatever equipment and supplies they brought with them. The plan was eventually cut down to just nine divisions landing on a narrower front and a single airborne division supporting them. This, in turn, caused outrage in the army, which thought that the narrower front was going to be suicide as it would be easily surrounded by the British defenders.
German soldiers boarding rubber dinghies for an invasion exercise
(Photo: Bundesarchiv)
A further problem with the barges was their poor maneuverability and unseaworthiness. They were supposed to cross the Channel in columns, then wheel around and position themselves parallel to the coast. The barges were then to simultaneously turn toward the shore and make land – all at night, coordinated by loud hailers. A single exercise was held with 50 ships in daylight. One barge capsized while turning and one tug lost its tow. Another barge got too close to its adjacent vessel and all the soldiers rushed to the other side for safety; the sudden shift in load caused the barge to overturn. Half of the ships failed to get their troops ashore within an hour of the first landings, and several hit the shore sideways, unable to lower their ramps.
German soldiers rehearsing for the invasion
(Photo: Bundesarchiv)
Yet another problem with the landings was that the tide hits different parts of the English coast at different times. If all units tried to make landfall two hours after high tide, then forces at the western end of the broad front would have need to land six hours ahead of the troops attacking Dover in the east; this obviously would have robbed units of the east of the element of surprise. On the other hand, if all units landed at the same time, they would have hit the shore during different phases of the tide.
German mountain troops waiting to board requisitioned fishing boats
(Photo: Bundesarchiv)
The Kriegsmarine’s other big problem was that it had no way of standing up to the Royal Navy. It would have been hard-pressed to do so at the best of times, and a significant portion of its biggest and newest ships were either damaged or sunk during the invasion of Norway. (Read our earlier article) A deception operation, Unternehmen Herbstreise (“Operation Autumn Journey”) was conceived: a group of light cruisers would escort ocean liners acting as a fake invasion force headed for Scotland, while two heavy cruisers would attack Allied convoys in the Atlantic to further distract the Royal Navy from the true target of the invasion.
The German heavy cruiser Admiral Hipper shortly after VE Day – it was supposed to be one of the two heavy cruisers used in the diversion
(Photo: Imperial War Museums)
Another option Germany might have had was the French fleet. The fleet, one of the largest and most modern at the time, was interred at Toulon in France and Mers-el-Kébir in French Algeria. Had the Germans crewed those ships and sailed out, the force might have kept the Royal Navy very busy in the mediterranean, forcing the Home Fleet to send some of its heavier ships to aid the Mediterranean Fleet. Unfortunately for Germany, the Royal Navy attacked the fleet at Mers-el-Kébir in early July, 1940, exactly to prevent something like that from happening, and sunk many of its ships.
A French battleship (either the Dunkerque or the Strasbourg) under fire during the British attack on the interred French fleet
(Photo: Jacques Mulard)
In the end, the Kriegsmarine had to rely on minefields, submarines and attack boats to keep the Royal Navy away from the invasion fleet. Of course, the minefields were quickly dismantled by the large number of British minesweepers, and the submarines and the torpedo boats would have been far too few to stop the Home Fleet, which would have sailed out in full force to stop a potential existential threat to Britain.
King George VI inspecting a German mine in 1939
German planners hoped that the Luftwaffe would lend a helping hand, but failed to consider that the German air force’s previous performance against enemy shipping was very disheartening, as it had neither the equipment (such as armor-piercing bombs) nor the training to reliably hit and damage moving vessels.
While the Kriegsmarine was busy gathering and modifying transport ships, the army did its best to help the landing troops with two types of amphibious tanks. The Tauchpanzer (“diving tank”) was a Panzer III or IV
(Read our earlier article) made waterproof by sealing all openings with tape or caulk. These would deploy directly into water up to 49 feet (15 meters) deep and roll along the seafloor until they got to the shore. At least in theory, since stopping (for example due to hitting a boulder or a trench) made them sink into the seabed. Once ashore, all the seals would be quickly removed by explosive tape, allowing the tank to fight. The Schwimmpanzer (“swimming tank”) was a Panzer II equipped with buoyancy boxes and propellers so it could swim to shore.
A Tauchpanzer about to be lowered into the water
(Photo: Bundesarchiv)
As for the Luftwaffe, they just failed. The entire operation hinged on the German air force suppressing the RAF and thus preventing the landing forces from being strafed and bomb at will. That suppression did not manifest. There were numerous reasons for why Germany lost the Battle of Britain; one main cause was that once the RAF started bombing Berlin in late August 1940, Göring had to shift his strategy from bombing RAF bases and production facilities to reprisal attacks against London and other population centers, and this allowed the RAF to build its numbers back up. Another problem was the lack of long-range escort fighters to accompany Luftwaffe bombers over Britain, as the Bf 109 couldn’t carry enough fuel (Read our earlier article). And underlying it all was the Luftwaffe’s gross underestimation of the RAF’s strength – on September 19, they believed the RAF had 140 frontline fighters, while the actual number was 700.
A German Heinkel He 111 bomber on a raid over East London
(Photo: Imperial War Museums)
Meanwhile, on the other side of the Channel, the possibility of an invasion, no matter how remote in practice, galvanized British fighting spirit as Churchill’s rhetoric turned the vague threat into a call to arms. An American journalist noted “To me it seems that this country is ten years younger than it was ten days ago.”
British Home Guard soldiers preparing a roadblock in York by inserting metal poles into pre-dug holes, late 1941
(Photo: Imperial War Museums)
In the end, September 1940 came and went, and the invasion never kicked off, largely due to Göring’s inability to take the RAF out of the picture. Hitler released forces set aside for the invasion in mid-October so they could be used elsewhere. The idea was kept on the table throughout 1941, but it was clearly not going to happen, and Hitler ordered all preparation for the invasion of Britain to cease in September 1941, a year after it was supposed to begin.

Veterans Day Promotion

$500 discount on all tours

WWII veterans celebrated in Normandy
(Photo: Author’s own)
On the occasion of the upcoming Veterans Day, we are offering all our available tours with a discount of $500 if you book and pay in full until November 11, 2023. Note that this offer applies only in case of new bookings, and it cannot be combined with other special promotions. If you have any questions related to this promotion or our tours, feel free to contact our travel consultants at 
Book now
Hear from our Passengers
Facebook Facebook
Instagram Instagram
Website Website
YouTube YouTube
Copyright © *|CURRENT_YEAR|* *|LIST:COMPANY|*, All rights reserved.

Our mailing address is:

Want to change how you receive these emails?
You can update your preferences or unsubscribe from this list.

up to30%
Beaches of Normandy Tours review
"It was truly amazing, I would definitely recommend BoN"D-Day Anniversary Tour, 2023
Beaches of Normandy Tours review
"It was everything I could have hoped for and more"Band of Brothers Tour, 2023
Beaches of Normandy Tours review
"I would recommend it to anyone who has an interest in history that changed the world"D-Day Anniversary Tour, 2023
4.9 - 235 reviews