Operation Sealion
Operation Sealion (
Unternehmen ("Undertaking") Seelöwe in
German) was a
World War II German plan to invade the
United Kingdom. It was never carried out.
Preparations began after the
Fall of France, when the Germans felt they had already won the war in the west. The UK, however, refused to respond to
peace talks, so more direct measures to break British resistance were considered.
Großadmiral Erich Raeder of the
Kriegsmarine was responsible for the creation of numerous studies for a German naval assault across the
English Channel. The earliest of these, made around November
1939, outlined the conditions that had to be met beforehand:
#The enemy naval forces must be eliminated or unable to intervene#
Royal Air Force air strength must be eliminated#Coastal defences must be destroyed#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
Channel, from
Dorset to
Kent. Final plans were much more modest, calling for nine
divisions to land by sea, around 67,000 men in the first echelon, and an airborne division to support them.
[Schenck, Peter C., Invasion of England 1940: The Planning of Operation Sealion, p. 231. Conway, London, 1990. ISBN 0-85177-548-9] 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.
[The Illustrated History of World War II by Owen Booth and John Walton. 1998. Page 70.] German forces would secure England up to the 52nd degree latitude, anticipating that the rest of the United Kingdom would then surrender.
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".
[Hall, Mark M: "Irish Secret's.", page 102. Irish Academic Press, 2003]The pre-conditions 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 put the responsibility for Sealion's success on the shoulders of
OKM Großadmiral Erich Raeder and
OKL Reichsmarschall Herman Göring.
The operation was postponed on
September 17th,
1940. On
12 October 1940, it was rescheduled for the spring of 1941. Despite the postponement, Hitler remained confident the UK would surrender once Russia was defeated and launched
Operation Barbarossa in
1941. The UK would then be isolated in Europe with no allies. The entry of the
United States into the war, however, and the reversal at
Moscow, meant that the window of opportunity for Sealion's success was closing. The failure to resolve the situation in the west would fulfil O.K.H.'s earlier warning of the dangers of a "two-front war". On
13 February 1943, after a conversation with Raeder,
Adolf Hitler finally abandoned the idea of invading Britain.
During the aerial battle,
RAF Bomber Command had been targeting the barges at their moorings in places such as
Rotterdam sending over bombers and sinking several.
The
Battle of Britain was part of
Operation Eagle (
Unternehmen Adler in German), originally intended by the
Luftwaffe to achieve
air superiority over the Royal Air Force and allow the invasion
fleet to cross the English Channel. However, the change in emphasis of the bombing from RAF bases to London (
the Blitz) turned it into a
strategic bombing operation. This switch afforded the Royal Air Force, reeling from Luftwaffe attacks further inland, time to pull back and regroup.
It is important to remember that Air Superiority is a fluid concept and can change according to which side has the greater air power in any particular area at any particular time. This is distinctly different to the concept of Total Air Superiority, which describes the strategic advantage of a nation with considerable airpower over that of a nation without a substantial airforce. This advantage can take the form of technological superiority (including air-speed, bomber payload, range), or simply the mobilization of greater numbers of aircraft.
British intelligence falsely believed that the Luftwaffe had a 4:1 advantage in the air. 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
radar to meet its trial under fire.
The main difficulty for the Wehrmacht was the complete 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 damage. In particular losses of destroyers were crippling. Also, the
U-boats, the most powerful arm of the Kreigsmarine, were not suitable for operations in the comparatively shallow and restricted English Channel . Although the Royal Navy could not bring the whole of its tenfold superiority against the Kriegsmarine to bear, as most of the fleet was engaged in the
Atlantic and
Mediterranean, the
British Home Fleet still had a very large advantage in numbers. This point cannot be over stressed as the difference in power between the British and German naval forces, together with the 22 miles of the English Channel, probably made the invasion unviable regardless of victory or defeat in the air during in the Battle Of Britain. In addition, the Kriegsmarine allocated its few remaining larger and more modern ships to diversionary operations in the
North Sea.
The British naval advantage became threatened when France surrendered. The French Fleet, one of the most powerful and modern in the world, if operated by the Kriegsmarine, could have tipped the balance against Britain, hence the criticality of its fate and the consequent
British action at Mers-el-Kebir.
It is also important to note that the transport ships to be used were, amongst others, primarily river
barges, as the Germans had no specialised 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.
Most current military analysts do not believe that Operation Sealion would have succeeded if undertaken, although some like
Micheal Burleigh and
Andrew Mollo believe it could. In fact
Adolf Galland has been quoted 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. It should be remembered that the D Day landings in 1944 were a close run thing and that was with years of preparation, the largest invasion force ever assembled, total Air and Naval superiority and the Germans having to fight in occupied France.
In addition, the losses in men and material suffered by the German airborne troops over the Low Countries in May during the
Battle of the Netherlands could not be replaced in time for the planned 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
The Black Book after the war) of 2,820 people to be arrested immediately.
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 forced to
surrender.
[The Sandhurst wargame was fictionalised in Richard Cox (ed.), Operation Sealion (London: Thornton Cox, 1974. ISBN 0-902726-17X). An analysis by F-K von Plehwe, "Operation Sealion 1940", was published in the Journal of the Royal United Services Institution, March, 1973.]*
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*
Operation Green (Ireland) - The planned German invasion of Ireland.
*
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.
