Operation Sea Lion

Operation Sea Lion
Part of World War II
Date 1940 Location Germany, Great Britain Result Abandoned
Belligerents
United Kingdom	Germany
Commanders and leaders
Lord Gort Hugh Dowding John Tovey	Gerd von Rundstedt Hermann Göring Erich Raeder
Strength
British Home Guard Home Fleet RAF Fighter Command	160,000
Casualties and losses
None	None

Operation Sealion (Unternehmen Seelöwe in German) was a World War II Nazi German plan to invade the United Kingdom, beginning in 1940. The operation was abandoned in September 1940.

Following swift victory in the Battle of France, Germany believed the war in the West was won. However, the United Kingdom refused peace talks. As a result, more direct measures to break British resistance were considered.

Großadmiral Erich Raeder of the Kriegsmarine oversaw numerous studies for a German naval assault across the English Channel. The earliest of these, made around November 1939, identified the conditions for invasion:

1. The Royal Navy must be eliminated.
2. Royal Air Force air strength must be eliminated.
3. Coastal defences must be destroyed.
4. British submarine action against landing forces must be prevented.

The Oberkommando des Heeres (OKH) originally planned an invasion on a vast scale, extending along most of the English Channel, from Dorset to Kent. Final plans were more modest, calling for nine divisions to land by sea with around 67,000 men in the first echelon and an airborne division to support them. The chosen invasion sites ran from Rottingdean in the west to Hythe in the east.

The battle plan called for German forces to be launched from Cherbourg to Lyme Regis, Le Havre to Ventnor and Brighton, Boulogne to Eastbourne, Calais to Folkestone, and Dunkirk and Ostend to Ramsgate. German paratroopers would land near Brighton and Dover. Once the coastline was secured, they would push north, taking Gloucester and encircling London. German forces would secure England up to the 52nd parallel, anticipating that the rest of the United Kingdom would then surrender.

Plan of Operation Sealion.

Hitler's initial warning order of 16 July 1940 reflected the most current thinking, and set out the revised minimum pre-conditions. He prefaced his order by stating:

• "I have decided to prepare a landing operation against England, and if necessary to carry it out".

Hitler's conditions for invasion were:

• The RAF was to be "beaten down in its morale and in fact, that it can no longer display any appreciable aggressive force in opposition to the German crossing".
• The English Channel was to be swept of British mines at the crossing points and the Straits of Dover must be blocked at both ends by German mines.
• The coastal zone between occupied France and England must be dominated by heavy artillery.
• The Royal Navy must be sufficiently engaged in the North Sea and the Mediterranean so that it could not intervene in the crossing. English home squadrons must be damaged or destroyed by air and torpedo attacks.

This placed responsibility for Sealion's success on the shoulders of OKM Großadmiral Erich Raeder and Oberkommando der Luftwaffe (OKL) Reichsmarschall Herman Göring.

Operation Eagle and air superiority

The aerial battles which resulted due to Operation Eagle ('Unternehmen Adler in German), later became known as the Battle of Britain. Eagles objective was for the Luftwaffe to achieve air superiority over the Royal Air Force (RAF) and allow the German invasion fleet to cross the English Channel. However, the change in emphasis of the bombing from RAF bases to bombing London (the Blitz) turned Eagle into a strategic bombing operation. This switch afforded the RAF, reeling from Luftwaffe attacks further inland, time to pull back and regroup.

British intelligence erroneously believed that the Luftwaffe had a 4:1 advantage in air superiority. This led to the Royal Air Force mobilizing the last of its reserves and accelerating the rate of Spitfire production. In addition, the threat of invasion allowed a new technology, radar, to be tested in the field.

The naval situation

The main difficulty for the Wehrmacht was the overwhelming disparity between the two navies. The Kriegsmarine had lost most of its large modern surface units in the Norwegian campaign, either as complete losses, or due to battle damage. In particular, losses of destroyers were crippling. The U-boats, the most powerful arm of the Kriegsmarine, were not suitable for operations in the relatively shallow and restricted English Channel. Although the Royal Navy could not bring the whole of its naval superiority against the Kriegsmarine to bear (most of the fleet was engaged in the Atlantic and Mediterranean) the British Home Fleet still had a very large advantage in numbers. The difference in power between the British and German naval forces, together with the 22-mile width of the English Channel, made the amphibious invasion plan very risky, regardless of victory or defeat in the air during the Battle of Britain. In addition, the Kriegsmarine had allocated its few remaining larger and modern ships to diversionary operations in the North Sea.

The French fleet, one of the most powerful and modern in the world, might have tipped the balance against Britain if operated by the Kriegsmarine. The destruction of the French fleet by the British during the attack on Mers-el-Kébir, as well as the scuttling of the French fleet in Toulon two years later, ensured that this could never occur.

Even had the Royal Navy been neutralised, the chances of making a successful amphibious invasion across the channel were remote. The transport ships to be used by the Germans for landing were primarily river barges, as the Germans had no specialized landing craft. This would have limited the quantity of artillery and tanks that could have been transported, and restricted operations to times of good weather. They were not designed for the open sea in any event. Nor were there enough barges to transport the first invasion wave, and the following waves and their equipment. Without specialised landing craft, the Germans would have needed to have immediately captured one of the ports, an unlikely situation considering the strength of the British coastal defences around the south-eastern harbours at that time.

Cancellation of the Operation

On 17 September 1940, Hitler held a meeting with Reichsmarschall Hermann Göring and Field Marshal Gerd von Rundstedt. Hitler became convinced that the operation was doomed. Control of the skies was unavailable, and coordination between three branches of the Government was out of question. Later that day, Hitler ordered the cancellation of the operation.

Had Operation Sealion been launched, six Einsatzgruppen were to follow the invasion force to Great Britain. They were provided with a list (known as The Black Book after the war) of 2,820 people to be arrested immediately.

Chances of success

Military historians are divided on whether or not Operation Sealion might have succeeded; some (such as Michael Burleigh and Andrew Mollo) believe success was possible. German fighter pilot and commander of Germany's air fighting force Adolf Galland (who participated in the Sandhurst wargames, below) claimed that the invasion never had a realistic chance of success and that there was a palpable sense of relief in the German Wehrmacht when it was finally called off. Germany's difficulties on the eastern front created an enormous drain on Germany—one that made a potential large-scale invasion across the English Channel a dangerous and costly gamble.

After the London Blitz, Hitler lost focus on this operation (which was to attack the British navy first to then attack by land).

Post-war test of the plan

In wargames conducted at the Royal Military Academy Sandhurst in 1974, which assumed the Luftwaffe had not yet won air supremacy, the Germans were able to establish a beachhead in England by using a minefield screen in the English Channel to protect the initial assault. However, the German ground forces were delayed at the "Stop Lines" (e.g. the GHQ Line), a layered series of defensive positions that had been built, each a combination of British Home Guard troops and physical barriers. At the same time, the regular troops of the British Army were forming up. After only a few days, the Royal Navy was able to reach the Channel from Scapa Flow, cutting off supplies and blocking further reinforcement. Isolated and facing regular troops with armour and artillery, the invasion force was made to surrender.

See also

• British anti-invasion preparations of World War II
• Operation Sealion order of battle
• Operation Herkules - The planned German invasion of Malta
• Operation Tannenbaum - The planned German invasion of Switzerland
• Operation Felix - The planned German invasion of Gibraltar
• Fall Grün - The planned German invasion of Ireland.

Further reading

• Fleming, Peter (1957). Operation Sea Lion. New York: Simon & Schuster. ISBN 0330242113.
• Haining, Peter (2004). Where the eagle landed : the mystery of the German invasion of Britain, 1940. London: Robson. ISBN 1861057504.
• Kieser, Egbert (1987). Cassell Military Classics: Operation Sea Lion: The German Plan To Invade Britain, 1940. Sterling. ISBN 030435208X.

External links and references

• British Invasion Defences
• Operation Seelöwe directive No.16
• Why Sealion was not a (realistic) option (essay)
• Sealion: an orthodox view (includes quotes from participants)
• Operation Overlord V Operation Sealion comparison, available here.