Operation Sealion

Operation Sealion, also written as Operation Sea Lion (German: Unternehmen Seelöwe) was the invasion of the British Home Isles by the Axis Powers during World War II.

Planning the Operation

In September 1939, with the successful German invasion of Poland infringing on both the French and British Alliance with Poland, both countries declared war on Germany. On 9 October, Hitler's "Directive No. 6 for the Conduct of the War" planned an offensive to defeat these allies and "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".

With the prospect of the Channel ports falling under Kriegsmarine (German Navy) control, Grand Admiral (Großadmiral) Erich Raeder (head of the Kriegsmarine) attempted to anticipate the obvious next step that might entail and instructed his operations officer, Captain (Kapitän) Hansjürgen Reinicke, to draw up a document examining "the possibility of troop landings in England should the future progress of the war make the problem arise". Reinicke spent five days on this study and set forth the following prerequisites that would eventually bloom into the directive Hitler would emphasise

The following conditions for the invasion to occur:

• The Royal Air Force (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 Strait 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. British home squadrons must be damaged or destroyed by air and torpedo attacks.

On 22 November 1939, the Head of Luftwaffe (German Air Force) Intelligence Joseph "Beppo" Schmid presented his "Proposal for the Conduct of Air Warfare", which argued for a counter to the British blockade and said "Key is to paralyse the British trade" by blocking imports to Britain and attacking seaports.

The OKW (Oberkommando der Wehrmacht or "High Command of the Armed Forces") considered the options and Hitler's 29 November "Directive No. 9 – Instructions For Warfare Against The Economy of the Enemy" stated that once the coast had been secured, the Luftwaffe and Kriegsmarine were to blockade UK ports with sea mines, attack shipping and warships, and make air attacks on shore installations and industrial production. This directive remained in force in the first phase of the Battle of Britain.

In December 1939, the German Army issued its own study paper (designated Nordwest) and solicited opinions and input from both the Kriegsmarine and the Luftwaffe. The paper outlined an assault on England's eastern coast between The Wash and the River Thames by troops crossing the North Sea from ports in the Low Countries. It suggested airborne troops as well as seaborne landings of 100,000 infantry in East Anglia, transported by the Kriegsmarine, which was also to prevent Royal Navy ships from getting through the Channel, while the Luftwaffe had to control airspace over the landings.

The Kriegsmarine response was focused on pointing out the many difficulties to be surmounted if invading England was to be a viable option. It could not envisage taking on the Royal Navy Home Fleet and said it would take a year to organise shipping for the troops. Reichsmarschall Hermann Göring, head of the Luftwaffe, responded with a single-page letter in which he stated, "[A] combined operation having the objective of landing in England must be rejected. It could only be the final act of an already victorious war against Britain as otherwise the preconditions for success of a combined operation would not be met".

Germany's swift and successful occupation of France and the Low Countries gained control of the Channel coast, facing what Schmid's 1939 report called their "most dangerous enemy". Raeder met Hitler on 21 May 1940 and raised the topic of invasion, but he warned of the risks and expressed a preference for blockade by air, submarines and raiders.

By the end of May, the Kriegsmarine had become even more opposed to invading Britain following its costly victory in Norway; after Operation Weserübung, the Kriegsmarine had only one heavy cruiser, two light cruisers, and four destroyers available for operations. Raeder was strongly opposed to Sea Lion, for over half of the Kriegsmarine surface fleet had been either sunk or badly damaged in Weserübung, and his service was hopelessly outnumbered by the ships of the Royal Navy.

In 1940, after the success of Fall Gelb, Operation Weserübung and the Polish Campaign, Britain was alone in its fight against the Nazis. Throughout July the Germans continued with attempts to find a diplomatic solution. Despite efforts by Lord Halifax and British parliamentarians still arguing for peace negotiations, Prime Minister Winston Churchill would reject all offers of peace with Nazi Germany, rather intending to fight to the very end.

The Reich would find itself given the first defeat it faced in the war, as the Luftwaffe was shot down over the skies of Britain in the vain attempt to destroy the RAF. Despite this setback however, plans for Operation Sealion would be shelved temporarily, as the Reich would go to war against the Soviet Union.

Execution

In 1943, seeing the fall of Russia, the Republic of Ireland decided to join in the Axis powers, invading Northen Ireland in early 1943. Taking advange of this new front and with most of the Royal Navy trapped in the Mediterrean or in the Pacific and without significant numbers of American warships near the British Isles, the Germans launched the largest amphibious assault in the history, Operation Sealion. The operation took place on the English Counties of Kent, West Sussex, East Sussex and the Isle of Wight around late 1943.

Whilst the invaders were desperate to keep the bridgehead and landing zones as wide and unassailable as possible, the defenders were scrambling to respond to the more immediate threat of the existing bridgeheads, attempting to forestall further landings and scrambling the Royal Air Force as best as could be managed, all whilst the immediate evacuation of senior government and the Royal Family was evacuated first to Scotland and later to Canada.

Despite their best attempts to cut the Axis supplies, the remnants of the Royal Navy and a handful of U.S Navy ships in the Atlantic were unable to defeat the Kriegsmarine and Regia Marina's naval superiority, and the Germans managed to secure their supplies lines and began attacking towards the rest of Great Britain. London fell in early 1944 and Allied morale having dealt multiple blows thusfar, collapsed. With the fall of London, multiple rebellions around the British Empire began, such as the Levant Uprising. With the constant stream of offensives by the Germans, the Allies were forced to retreat back to the Scottish Highlands, with cities such as Manchester, Glasgow and Edinburgh falling in quick succession. By April 1945, after a hasty evacuation by US Army Forces, the remaining troops left saw no other option and capitulated to the Germans.