|Operation Sea Lion|
|Part of the Western Front of the Second World War|
|Operational scope||Normandy, the Belgian coast line, the English Channel and the English coast line from Kent to Dorset, Isle of Wight and parts of Devon, but principally in Sussex and Kent.|
|Objective||Elimination of Great Britain as a base of military operations against the German Reich|
|Outcome||Eventual cancellation and diversion of German forces for Operation Barbarossa|
Operation Sea Lion (German language: Unternehmen Seelöwe) was Nazi Germany's plan to invade the United Kingdom during the Second World War following the Fall of France. For any likelihood of success, however, the operation required air and naval supremacy over the English Channel, neither of which the Germans ever achieved during or after the Battle of Britain. Sea Lion was postponed indefinitely on 17 September 1940 and never carried out.
Adolf Hitler had decided by early November 1939 on forcing a decision in the West by invading Belgium, the Netherlands and France. With the prospect of the Channel ports falling under Kriegsmarine (the German Navy) control, and attempting to anticipate the obvious next step that might entail, Grand Admiral (Großadmiral) Erich Raeder (head of the Kriegsmarine) instructed his operations officer, Kapitän Hans Jürgen 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:
- Elimination or sealing off of Royal Navy forces from the landing and approach areas.
- Elimination of the Royal Air Force (RAF).
- Destruction of all Royal Navy units in the coastal zone.
- Prevention of British submarine action against the landing fleet.
In December 1939, the German Army issued its own study paper (designated Nordwest) and solicited opinions and input from both the Kriegsmarine and Luftwaffe (the German Air Force). The paper outlined an assault on England's eastern coast between The Wash and the River Thames by troops crossing the North Sea from Low Country ports. 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." The Kriegsmarine response was rather more restrained but equally focused on pointing out the many difficulties to be surmounted if invading England was to be a viable option.
Later in the spring of 1940 the Kriegsmarine became even more opposed to invading Britain after its Pyrrhic victory in Norway. After Operation Weserübung, as the invasion of Norway had been code-named, the Kriegsmarine had only one heavy cruiser, two light cruisers, and four destroyers available for operations. Admiral Raeder was strongly opposed to Sea Lion since almost the entire 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.
On 16 July 1940, following Germany's swift and successful occupation of France and the Low Countries and growing impatient with Britain's outright rejection of his recent peace overtures, Hitler issued Führer Directive No. 16, setting in motion preparations for a landing in Britain. He prefaced the order by stating: "As England, in spite of her hopeless military situation, still shows no signs of willingness to come to terms, I have decided to prepare, and if necessary to carry out, a landing operation against her. The aim of this operation is to eliminate the English Motherland as a base from which the war against Germany can be continued, and, if necessary, to occupy the country completely."
Hitler's directive set four conditions for the invasion to occur:
- 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 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.
This ultimately placed responsibility for Sea Lion's success squarely on the shoulders of Raeder and Göring, neither of whom had the slightest enthusiasm for the venture and, in fact, did little to hide their opposition to it. Nor did Directive 16 provide for a combined operational headquarters under which all three service branches (Army, Navy, Air Force) could work together under a single umbrella organisation to plan, coordinate and execute such a complex undertaking (similar to the Allies' creation of the Supreme Headquarters Allied Expeditionary Force (SHAEF) for the later Normandy landings).
Upon hearing of Hitler's intentions, Italian dictator Benito Mussolini, through his Foreign Minister Count Galeazzo Ciano, quickly offered up to ten divisions and thirty squadrons of Italian aircraft for the proposed invasion. Hitler initially declined any such aid but eventually allowed a small contingent of Italian fighters and bombers, the Italian Air Corps (Corpo Aereo Italiano or CAI), to assist in the Luftwaffe's aerial campaign over Britain in October/November 1940.
German land forces
Battle of Britain
Beginning in August 1940, the German Luftwaffe began a series of concentrated aerial attacks (designated Unternehmen Adlerangriff or Operation Eagle Attack) on targets throughout the United Kingdom in an attempt to destroy the RAF and establish air superiority over Great Britain. The campaign later became known as the Battle of Britain. The change in emphasis of the bombing from RAF bases to bombing London, however, turned Adler into a strategic bombing operation. The effect of the switch in strategy is disputed. Some historians argue that the change in strategy lost the Luftwaffe the opportunity of winning the air battle, or air superiority. Others argue the Luftwaffe achieved little in the air battle and the RAF was not on the verge of collapse, as often claimed. Another perspective has also been put forward, which suggests the Germans could not have gained air superiority before the weather window closed. Others have pointed out that it was unlikely the Luftwaffe was ever able to destroy RAF Fighter Command. If British losses became severe, the RAF could simply have withdrawn northward and regrouped. It could then deploy when, or if, the Germans launched an invasion. Some also venture to argue Sea Lion would have failed regardless, because of the weaknesses of German sea power.
The view of those that believe, regardless of a potential German victory in the air battle, Sea Lion was still not going to succeed included a number of German General Staff members. Grand Admiral Karl Dönitz believed air superiority was "not enough". Dönitz stated, "we possessed neither control of the air or the sea; nor were we in any position to gain it". Erich Raeder, commander-in-chief of the Kriegsmarine in 1940 argued:
.....the emphatic reminder that up until now the British had never thrown the full power of their fleet into action. However, a German invasion of England would be a matter of life and death for the British, and they would unhesitatingly commit their naval forces, to the last ship and the last man, into an all-out fight for survival. Our Air Force could not be counted on to guard our transports from the British Fleets, because their operations would depend on the weather, if for no other reason. It could not be expected that even for a brief period our Air Force could make up for our lack of naval supremacy.
When Franz Halder, the Chief of the Army General Staff, heard of the state of the Kriegsmarine, and its plan for the invasion, he noted in his diary, on 28 July 1940, "If that [the plan] is true, all previous statements by the navy were so much rubbish and we can throw away the whole plan of invasion".
Alfred Jodl, Chief of Operations in the OKW (Oberkommando der Wehrmacht), remarked, after Raeder said the Kriegsmarine could not meet the operational requirements of the Army, "then a landing in England must be regarded as a sheer act of desperation".
Limitations of the Luftwaffe
The track record of the Luftwaffe against naval combat vessels up to that point in the war was poor. In the Norwegian Campaign, despite eight weeks of continuous air supremacy, the Luftwaffe sank only two British warships. The German aircrews were not trained or equipped to attack fast-moving naval targets, particularly agile naval destroyers or Motor Torpedo Boats (MTB). The Luftwaffe also lacked armour-piercing bombs and had almost no aerial torpedo capability, essential for defeating larger warships. The Luftwaffe made 21 deliberate attacks on small torpedo boats during the Battle of Britain, sinking none. The British had between 700 and 800 small coastal craft (MTBs, MGBs (Motor Gun Boats) and smaller vessels), making them a critical threat if the Luftwaffe could not deal with the force. Only nine MTBs were lost to air attack out of 115 sunk by various means throughout the Second World War. Only nine destroyers were sunk by air attack in 1940, out of a force of over 100 operating in British waters at the time. Only five were sunk while evacuating Dunkirk, despite large periods of German air superiority, thousands of sorties flown, and hundreds of tons of bombs dropped. The Luftwaffe's record against merchant shipping was also not impressive. It sank only one in every 100 British vessels passing through British waters in 1940. Moreover, most of this total was achieved using mines.
Luftwaffe Special Equipment
Had an invasion taken place the Me 110 equipped Erprobungsgruppe 210 would have dropped ‘Seilbomben' just prior to the landings. This was a secret weapon which would have been used to blackout the electricity network in the south-east of England. The equipment for dropping the wires was fitted to the Me 110 aeroplanes and tested. Basically it involved dropping wires across high voltage wires, and was probably as dangerous to the crews of the aircraft as it was to the British.
The most daunting problem for Germany in protecting an invasion fleet was the small size of its navy. The Kriegsmarine, already numerically far inferior to Britain's Royal Navy, had lost a sizeable portion of its large modern surface units in April 1940 during the Norwegian Campaign, either as complete losses or due to battle damage. In particular, the loss of two light cruisers and ten destroyers was crippling, as these were the very warships most suited to operating in the Channel narrows where the invasion would likely take place. Most U-boats, the most powerful arm of the Kriegsmarine, were meant for destroying ships, not supporting an invasion.
Although the Royal Navy could not bring to bear the whole of its naval superiority as most of the fleet was engaged in the $3 and Mediterranean, the British Home Fleet still had a very large advantage in numbers. It was debatable whether British ships were as vulnerable to enemy air attack as the Germans hoped. During the Dunkirk evacuation few warships were actually sunk, despite being stationary targets. The overall disparity between the opposing naval forces made the amphibious invasion plan risky, regardless of the outcome in the air. In addition, the Kriegsmarine had allocated its few remaining larger and modern ships to diversionary operations in the North Sea.
The fleet of defeated France, one of the most powerful and modern in the world, might have tipped the balance against Britain if captured by the Germans. However, the pre-emptive destruction of the French fleet by the British at Mers-el-Kébir, and the scuttling of the French fleet in Toulon two years later, ensured that this could not happen.
Even if the Royal Navy had been neutralised, the chances of a successful amphibious invasion across the Channel were remote. The Germans had no specialised landing craft, and had to rely primarily on river barges to lift troops and supplies for the landing. This would have limited the quantity of artillery and tanks that could be transported and restricted operations to times of good weather. The barges were not designed for use in open sea and, even in almost perfect conditions, they would have been slow and vulnerable to attack. There were also not enough barges to transport the first invasion wave nor the following waves with their equipment. The Germans would have needed to immediately capture a port, an unlikely circumstance considering the strength of the British coastal defences around the south-eastern harbours at that time. The British also had several contingency plans, including the use of poison gas.
In 1940 the German Navy was ill-prepared for mounting an amphibious assault the size of Operation Sea Lion. Lacking purpose-built landing craft and both doctrinal and practical experience with amphibious warfare, the Navy was largely starting from scratch. Some efforts had been made during the inter-war years to investigate landing military forces by sea, but inadequate funding severely limited any useful progress.
The Navy had taken some small steps in remedying the landing craft situation with construction of the Pionierlandungsboot 39 (Engineer Landing Boat 39), a self-propelled shallow-draft vessel which could carry 45 infantrymen, two light vehicles or 20 tons of cargo and land on an open beach, unloading via a pair of clamshell doors at the bow. But by late September 1940 only two prototypes had been delivered.
Recognising the need for an even larger craft capable of landing both tanks and infantry onto a hostile shore, the Navy began development of the 220-ton Marinefährprahm (MFP) but these too were unavailable in time for a landing on English soil in 1940, the first of them not being commissioned until April 1941.
Given barely two months to assemble a large seagoing invasion fleet, the Kriegsmarine opted to convert inland river barges into makeshift landing craft. Approximately 2,400 barges were collected from throughout Europe (860 from Germany, 1,200 from the Netherlands and Belgium and 350 from France). Of these, only about 800 were powered (some insufficiently); the rest had to be towed by tugs.
Two types of inland river barge were generally available in Europe for use in Sea Lion: the peniche, which was 38.5 metres long and carried 360 tons of cargo, and the Kampine, which was 50 metres long and carried 620 tons of cargo. Of the barges collected for the invasion, 1,336 were classified as peniches and 982 as Kampinen. For simplicity’s sake, the Germans designated any barge up to the size of a standard peniche as Type A1 and anything larger as Type A2.
Converting the assembled barges into landing craft involved cutting an opening in the bow for off-loading troops and vehicles, welding longitudinal I-beams and transverse braces to the hull to improve seaworthiness, adding a wooden internal ramp and pouring a concrete floor in the hold to allow for tank transport. As modified, the Type A1 barge could accommodate three medium tanks while the Type A2 could carry four.
This barge was a Type A altered to carry and rapidly off-load the submersible tanks (Tauchpanzer) developed for use in Sea Lion. They had the advantage of being able to unload their tanks directly into water up to 15 metres (49 ft) in depth, several hundred yards from shore, whereas the unmodified Type A had to be firmly grounded on the beach, making it more vulnerable to enemy fire. The Type B required a longer external ramp (11 metres) with a float attached to the front of it. Once the barge anchored, the crew would extend the internally stowed ramp using block and tackle sets until it was resting on the water's surface. As the first tank rolled forward onto the ramp, its weight would tilt the forward end of the ramp into the water and push it down onto the seabed. Once the tank rolled off, the ramp would bob back up to a horizontal position, ready for the next one to exit. The Navy High Command increased its initial order for 60 of these vessels to 70 in order to compensate for expected losses. A further five were ordered on 30 September as a reserve.
The Type C barge was specifically converted to carry the Panzer II amphibious tank (Schwimmpanzer). Because of the extra width of the floats attached to this tank, cutting a broad exit ramp into the bow of the barge was not considered advisable as it would have compromised the vessel's seaworthiness to an unacceptable degree. Instead, a large hatch was cut into the stern, thereby allowing the tanks to drive directly into deep water before turning under their own motive power and heading towards shore. The Type C barge could accommodate up to four Schwimmpanzers in its hold. Approximately 14 of these craft were available by the end of September.
During the planning stages of Sea Lion, it was deemed desirable to provide the advanced infantry detachments (making the initial landings) with greater protection from small-arms and light artillery fire by lining the sides of a Type A barge with concrete. Wooden slides were also installed along the barge’s hull to accommodate ten assault boats (Sturmboote), each capable of carrying six infantrymen and powered by a 30 hp outboard motor. The extra weight of this additional armor and equipment reduced the barge’s load capacity to 40 tons. By mid-August, 18 of these craft, designated Type AS, had been converted, and another five were ordered on 30 September.
The Luftwaffe had formed its own special command (Sonderkommando) under Major Fritz Siebel to investigate the production of landing craft for Sea Lion. Major Siebel proposed giving the unpowered Type A barges their own motive power by installing a pair of 600 hp surplus BMW aircraft engines on them driving propellers. The Navy was highly sceptical of this venture but the Army high command enthusiastically embraced the concept and Siebel proceeded with the conversions.
The aircraft engines were mounted on a platform supported by iron scaffolding at the aft end of the vessel. Cooling water was stored in tanks mounted above-deck. As completed, the Type AF had a speed of six knots, and a range of 60 nautical miles unless auxiliary fuel tanks were fitted. Disadvantages of this set-up included an inability to back the vessel astern, limited maneuverability and the deafening noise of the engines which would have made voice commands problematic.
By 1 October, 128 Type A barges had been converted to airscrew propulsion and, by the end of the month, this figure had risen to over 200.
The Kriegsmarine later used some of the motorized Sea Lion barges for landings on the Russian-held Baltic islands in 1941 and, though most of them were eventually returned to the inland rivers they originally plied, a reserve was kept for military transport duties and for filling out amphibious flotillas.
Providing armour support for the initial wave of assault troops was a critical concern for Sea Lion planners and much effort was devoted to finding practical ways of rapidly getting tanks onto the invasion beaches. Though the Type A barges could disembark several medium tanks onto an open beach, this could be accomplished only at low tide when the barges were firmly grounded. The time needed for assembling the external ramps also meant that both the tanks and the ramp assembly crews would be exposed to close-quarter enemy fire for a considerable time. A safer and faster method was needed and the Germans eventually settled on providing some tanks with floats and making others fully submersible.
The Schwimmpanzer II was a modified version of the Panzer II which, at 8.9 tons, was light enough to float with the attachment of long rectangular buoyancy boxes on each side of the tank's hull. The boxes were machined from aluminium stock and filled with Kapok sacks for added buoyancy. Motive power came from the tank's own tracks which were connected by rods to a propeller shaft running through each float. The Schwimmpanzer II could make 5.7 km/h in the water. An inflatable rubber hose around the turret ring created a waterproof seal between the hull and turret. The tank's 2 cm gun and coaxial machinegun were kept operational and could be fired while the tank was still making its way ashore. Because of the great width of the pontoons, Schwimmpanzer IIs were to be deployed from specially-modified Type C landing barges, from which they could be launched directly into open water from a large hatch cut into the stern. The Germans converted 52 of these tanks to amphibious use prior to Sealion's cancellation.
The Tauchpanzer or deep-wading tank (also referred to as the U-Panzer or Unterwasser Panzer) was a standard Panzer III or Panzer IV medium tank with its hull made completely waterproof by sealing all sighting ports, hatches and air intakes with tape or caulk. The gap between the turret and hull was sealed with an inflatable hose while the main gun mantlet, commander’s cupola and radio operator’s machine gun were given special rubber coverings. Once the tank reached the shore, all covers and seals could be blown off via explosive cables, enabling normal combat operation.
Fresh air for both the crew and engine was drawn into the tank via an 18m long rubber hose to which a float was attached to keep one end above the water’s surface. A radio antenna was also attached to the float to provide communication between the tank crew and the transport barge. The tank's engine was converted to be cooled with seawater, and the exhaust pipes were fitted with over-pressure valves. Any water seeping into the tank's hull could be expelled by an internal bilge pump. Navigation underwater was accomplished using a directional gyro compass or by following instructions radioed from the transport barge.
Experiments conducted at the end of June and early July at Schilling, near Wilhelmshaven, showed that the submersible tanks functioned best when they were kept moving along the seabed as, if halted for any reason, they tended to sink into the sand. Obstacles such as underwater trenches or large rocks tended to stop the tanks in their tracks, and it was decided for this reason that they should be landed at high tide so that any mired tanks could be retrieved at low tide. Submersible tanks could operate in water up to a depth of 15 metres (49 ft).
The Kriegsmarine initially expected to use 50 specially-converted motor coasters to transport the submersible tanks, but testing with the coaster Germania showed this to be impractical. This was due to the ballast needed to offset the weight of the tanks, and the requirement that the coasters be grounded to prevent them from capsizing as the tanks were transferred by crane onto the vessel's wooden side ramps. These difficulties led to development of the Type B barge.
By the end of August the Germans had converted 160 Panzer IIIs, 42 Panzer IVs and 52 Panzer IIs to amphibious use. This gave them a paper strength of 254 machines, about the equivalent of an armoured division. The tanks were divided into four battalions or detachments labeled Panzer-Abteilung A, B, C and D. They were to carry sufficient fuel and ammunition for a combat radius of 200 km.
Specialised landing equipment
As part of a Navy competition, prototypes for a prefabricated "heavy landing bridge" or jetty (similar in function to later Allied Mulberry Harbours) were designed and built by Krupp Stahlbau and Dortmunder Union and successfully overwintered in the North Sea in 1941–42. Krupp's design won out, as it only required one day to install, as opposed to twenty-eight days for the Dortmunder Union bridge. The Krupp bridge consisted of a series of 32m-long connecting platforms, each supported on the seabed by four steel columns. The platforms could be raised or lowered by heavy-duty winches in order to accommodate the tide. The German Navy initially ordered eight complete Krupp units composed of six platforms each. This was reduced to six units by the autumn of 1941, and eventually cancelled altogether when it became apparent that Sea Lion would never take place.
In mid-1942, both the Krupp and Dortmunder prototypes were shipped to the Channel Islands and installed together off Alderney, where they were used for unloading materials needed to fortify the island. Referred to as the "German jetty" by local inhabitants, they remained standing for the next thirty-six years until demolition crews finally removed them in 1978–79, a testament to their durability.
The German Army developed a portable landing bridge of its own nicknamed Seeschlange (Sea Snake). This "floating roadway" was formed from a series of joined modules that could be towed into place to act as a temporary jetty. Moored ships could then either unload their cargo directly onto the roadbed or lower it down onto waiting vehicles via their heavy-duty booms. The Seeschlange was successfully tested by the Army Training Unit at Le Havre in France in the autumn of 1941 and later chosen for use in Operation Herkules, the proposed Italo-German invasion of Malta. It was easily transportable by rail.
A specialised vehicle intended for Sea Lion was the Landwasserschlepper (LWS), an amphibious tractor under development since 1935. It was originally intended for use by Army engineers to assist with river crossings. Three of them were assigned to Tank Detachment 100 as part of the invasion; it was intended to use them for pulling ashore unpowered assault barges and towing vehicles across the beaches. They would also have been used to carry supplies directly ashore during the six hours of falling tide when the barges were grounded. This involved towing a Kässbohrer amphibious trailer capable of transporting 10–20 tons of freight behind the LWS. The LWS was demonstrated to General Halder on 2 August 1940 by the Reinhardt Trials Staff on the island of Sylt and, though he was critical of its high silhouette on land, he recognised the overall usefulness of the design. It was proposed to build enough tractors that one or two could be assigned to each invasion barge, but the late date and difficulties in mass-producing the vehicle prevented this.
Other equipment to be used for the first time
Operation Sealion would have been the first ever amphibious invasion by a mechanised army, and the largest amphibious invasion since Gallipoli. The Germans had to invent and improvise a lot of equipment. They also proposed to use some new weapons and use upgrades of their existing equipment for the first time. These included:
1. New anti-tank guns and ammunition. The standard German anti-tank gun, the 37mm Pak 36, was capable of penetrating the armour of all 1940 British tanks except the Matilda and Valentine. Armour piercing Ballistic capped (tungsten-cored) ammunition (Pzgr. 40) for 37 mm Pak 36 had become available in time for the invasion. The 37mm Pzgr.40 would still have had trouble penetrating the Matilda II’s armour  so the first echelon units replaced theirs with French or Czech 47mm guns (which weren't much better). The Pak 36 began to be replaced by the 50 mm Pak 38 in mid-1940. The Pak 38, which could penetrate a Matilda's armour, would probably have seen action first with Sealion as it would have been issued initially to the Waffen-SS and the army's elite units, and all those units were in the Sealion force. These included the Leibstandarte SS Adolf Hitler regiment, the Großdeutschland regiment, 2 Mountain, 2 Jäger, 2 Fallschirmjäger, 4 Panzer, and 2 Motorised Divisions. In addition the 7th Infantry division was considered the one of the best in the Heer, and the 35th almost as good.[not in citation given] .
2. Captured French armoured tractors. The use of these tractors by the first wave units was intended to reduce their dependence on horses and probably would have reduced the problems of getting supplies off the beaches. In addition to their proposed use on the beaches, the Germans later used them as tractors for anti-tank guns and munitions carriers, as self-propelled guns, and as armoured personnel carriers. There were two main types. The Renault UE Chenillette (German name: Infanterie Schlepper UE 630 (f)) was a light tracked armoured carrier and prime mover produced by France between 1932 and 1940. Five to six thousand were built, and about 3,000 were captured and overhauled by the Germans. They had a storage compartment that could carry 350 kg, pull a trailer weighing 775 kg for a total of about 1000 kg, and could climb a 50% slope. The armour was 5-9mm, enough to stop shell fragments and bullets. There was also the Lorraine 37L, which was larger, of which 360 fell into German hands. In that vehicle a load of 810 kilograms could be carried, plus a 690 kg trailer pulled for a total of 1.5 tonnes. The use of such captured equipment meant that the first wave divisions were largely motorised, with the first wave using 9.3% (4,200) of the 45,000 horses normally required .
Broad versus narrow front
The German Army High Command (Oberkommando des Heeres, OKH) originally planned an invasion on a vast scale, landing over forty divisions from Dorset to Kent. This was far in excess of what the Kriegsmarine could supply, and final plans were more modest, calling for nine divisions to make an amphibious landing in Sussex and Kent 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 German Navy wanted a front as short as possible as they regarded this as more defensible. Admiral Raeder wanted a front stretching from Dover to Eastbourne, stressing that shipping between Cherbourg/Le Havre and Dorset would be exposed to attacks from the Navy based in Portsmouth and Plymouth. General Halder rejected this, saying, "From the army's point of view I regard it as complete suicide, I might just as well put the troops that have landed straight through the sausage machine."<ref>Shears, David. Operation Sealion, There is a large corpus of works set in an alternate history where the German invasion of Britain is attempted or successfully carried out.
- Alien space bats – a discussion how Operation Sea Lion relates to the plausibility of alternate histories
- Auxiliary Units – Planned British resistance movement had a German invasion been successful
- Battle of Crete
- British anti-invasion preparations of World War II
- Cross-Channel guns in the Second World War
- Dunkirk Evacuation
- Operation Felix – The planned German invasion of Gibraltar
- Operation Grün – The planned German invasion of Ireland
- Operation Herbstreise, a planned series of deception operations to support the German invasion of the United Kingdom
- Operation Herkules – The planned German invasion of Malta
- Operation Overlord - The Allied invasion of Normandy, 1944
- Operation Tannenbaum – The planned German invasion of Switzerland
- RAF Fighter Command Order of Battle 1940
- Führer Directive 16
- David Shears, "Hitler’s D-Day", MHQ, vol. 6 Number 4 (Summer 1994)
- Ansel, p.43
- Ansel, pp.47–49
- Murray, Williamson & Millet, Alan A War To Be Won (Harvard: Belknap Press, 2000), p.66.
- Murray, Williamson & Millet, Alan A War To Be Won, Harvard: Belknap Press, 2000 page 84.
- Cox, p.159
- Cox, p.160
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- Macksey, Kenneth, Beda Fomm: The Classic Victory, p. 35. Ballantine, New York, 1971.
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- Bungay 2000, pp. 368–369.
- Hooton 2010, p. 80.
- Corum 1997, pp. 283–284.
- Dönitz 1958 (1997 edition), p. 114.
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- Greiner in Detweiler 1979, pp.10–12.
- World War II: Crucible of the Contemporary World : Commentary and Readings - Google Books. Books.google.co.uk. http://books.google.co.uk/books?id=3l_vg1p5EHsC&pg=PA374&lpg=PA374&dq=the+Luftwaffe+had+no+armour-+piercing+bombs,&source=bl&ots=dv54D3ux6z&sig=egiMswxvY8T_33c97nDVa67LB4k&hl=en&sa=X&ei=jAgkUZj9B9SyhAeLuICAAQ&ved=0CEcQ6AEwAg#v=onepage&q=the%20Luftwaffe%20had%20no%20armour-%20piercing%20bombs%2C&f=false. Retrieved 2013-04-08.
- Larew 1992, pp. 245–247.
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- Schenk, p.67
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- Schenk, pp.99–105
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- Alderney at War. Brian Bonnard. 1993.ISBN 0-7509-0343-0. pp106-108. Alan Sutton Publishing.
- Schenk, p.139
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- p. 183 Schenk
- Anthony Tucker-Jones, Hitlers Great Panzer Heist, Pen & Sword Books, 2007, p.59 & p. 155
- Schenk p. 183
- Peter Fleming says on page 229 that the number of horses was reduced to 4,200 for the first wave (466 per division) and 7,000 for the second wave.
- p. 185 Schenk
- p. 184 Schenk
- Schenk, p.231
- Ansel, Walter (1960). Hitler Confronts England. Duke University Press.
- Burdick, Charles, Jacobsen, Hans-Adolf. (1988). The Halder War Diary 1939–1942. Navatop Press, California. ISBN 1-85367-022-7
- Corum, James. The Luftwaffe: Creating the Operational Air War, 1918–1940. Kansas University Press. 1997. ISBN 978-0-7006-0836-2
- Cox, Richard (1977). Operation Sea Lion. Presidio Press. ISBN 0-89141-015-5
- Dönitz, Karl. Ten years and Twenty Days. New York: Da Capo Press, First Edition, 1997. ISBN 0-306-80764-5.
- Evans, Martin Marix (2004). Invasion! Operation Sealion 1940. Pearson Education. ISBN 0-582-77294-X
- Fleming, Peter (1957). Operation Sea Lion. Simon & Schuster. ISBN 0-330-24211-3
- Greiner, H. 'Operation Seelowe and Intensified Air Warfare Against England up to the 30 October 1940', in Detweiler, D. World War II German Military Studies, Volume 7 of 24 (New York, 1979)
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- Hooton, E.R.. Hooton, E.R. The Luftwaffe: A Study in Air Power, 1933–1945. Classic Publications, London. 2010. ISBN 978-1-906537-18-0
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- Raeder, Erich. Erich Rader, Grand Admiral: The Personal Memoir of the Commander in Chief of the German Navy From 1935 Until His Final Break With Hitler in 1943. New York: Da Capo Press. United States Naval Institute, 2001. ISBN 0-306-80962-1.
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|Wikimedia Commons has media related to Operation Seelöwe.|
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- Operation Sealion (The German Threat to Britain in World War Two by Dan Cruickshank, BBC)
- Kriegsmarine nautical charts, private collection (Italy)
- Operation Sealion (argues that it was just a bluff) - BBC Timewatch 1998
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