Sea Lion: 1940

Operation Sea Lion: Tiger or pussycat?

Churchill’s version of Operation Sea Lion, (Churchill p. 273).

Operation Sea Lion (Unternehemen Seelöwe), a proposed German invasion of England in 1940, was a battle never fought beyond its essential precursor (Unternehemen Adler, Operation Eagle Attack) that included the failed Battle of Britain. Would it have succeeded?

Influential authors, such as Kenneth Macksey (1980) and Michael Burleigh (2000) say Operation Sea Lion would have succeeded. Thornton Cox (1974), also Peter Fleming (2003), Derek Robinson (2005) and Stephen Bungay (2000), come to diametrically opposite conclusions. Macksey, a former tank major who became a military historian and biographer, and respected historian Dr Michael Burleigh conclude that a mid-July 1940 Operation Sea Lion probably would have been successful. Cox, a military correspondent with the Daily Telegraph, reports on a very persuasive and carefully structured 1974 Sandhurst war game, conducted by very senior Britons and Germans, most of whom would have been participants in the original battle. They reached a consensus outcome: German defeat. The defeat was attributed largely to inadequate German logistics, especially in the face of certain and effective RAF and RN interdiction.

Winston Churchill (Churchill 1949 pp. 247-278) offers substantial evidence and characteristically concludes that Britain would have repelled Sea Lion with massive German losses.

David Shears (Shears 2001a and 2001b) briefly analyses most of the important evidence and agrees with Churchill and Cox that three chief factors militated against a successful Sea Lion. They were: firstly, the inability of Admiral Raeder to find and train a large enough assault transport and logistics fleet in the ridiculously short time he was allowed; secondly, failure by Reichsmarshal Herman Göring to achieve control of the air (Unternehemen Adler, “the key to Sea Lion”, Shears 2001a p. 98); and thirdly, the time it took to emplace German cross-channel guns. Contributing to these factors must be Hitler’s vacillation about the project, the outstandingly successful British intelligence penetration of Sea Lion, simple meteorological factors that constrained any invasion timetable, and a potent temporal factor in that the longer it took to mount an assault after the nadir of Dunkirk (May-June 1940), the harder the British nut would become to crack.

Macksey assumptions

Macksey makes a number of key assumptions, for instance that Hitler, instead of hesitating, initiates resolute Sea Lion planning as early as May 1940. Over Raeder’s objections about RN and RAF dangers he then mounts a smaller scale assault by sea and air. Led by Luftwaffe paratroops, the German Army lands on a 25-mile stretch of coast between Hythe and Rye in mid-July. Demoralised defenders are unable to repulse the landings, the RN is unable to coordinate effective counterattacks with the RAF and refugees quickly clog the roads. Heavy RN warships summoned from Scotland and Gibraltar record some successes, but by and large everything is too little and too late to prevent a German victory. The royal family and cabinet evacuate to continue the fight from exile.

Cross-Channel logistics shortfall

Following Hitler’s initial 16 July Sea Lion directive, the German Army’s plan to land 100,000 soldiers required an assault invasion fleet of about 600,000 tons of seagoing shipping, more than half of the total available to Germany (Churchill p. 269-271). The second wave of 160,000 men and heavy equipment required 2,000,000 tons. At that time the Germans had no specialised landing craft, other than simple river-navigable vessels and very few Siebel catamarans.

Invasion barges pre-positioned in Wilhemshaven.

Many hundreds of unwieldy river barges, few capable of more than two or three knots, were requisitioned and even pre-positioned for loading, but they lacked the sea-keeping qualities required to navigate the English Channel safely and their slow speed gave the British ample warning of both assembly and attack. Channel currents of four to five knots presented a further obstacle. They also became lucrative RAF targets and the barges’ absence from their usual duties soon created serious problems for the German war-related transport system.

Fritz Siebel designed and manufactured fast catamaran ferries powered by old aircraft engines driving air or water propellers. They could carry 80 tons of cargo or troops. However, only 308 of these were built in all of 1940 and in September 1940 they posed little practical threat (Shears 2001a p. 89).

Transport interdiction

Good intelligence, together with RAF shipping reconnaissance, kept track of significant shipping movements. “When on September 1 the great southward movement of invasion shipping began, it was watched, reported and violently assailed by the Royal Air Force,” (Churchill p. 271). The German naval staff noted in its war diary that during the night of 14-15 September, the RAF inflicted “considerable casualties” on transports in Antwerp, including “five steamers heavily damaged … one barge sunk, two cranes destroyed, an ammunition train blown up, several sheds burning,” (Shears 2001a p. 100). Together, all this led to fairly accurate British threat assessments and potentially effective countermeasures. Without surprise, without adequate shipping and without Channel air and sea control, Sea Lion was indeed a very high risk operation.

Deploying some of his aircraft to newly captured airfields in late July, Göring aimed to achieve total air superiority over the Channel by bombing British radar and fighter airfields in the southeast into submission “within four days” and defeating the entire RAF “within two to four weeks”. Like later “Victory through Airpower” adherents, he even envisaged his Luftwaffe alone bombing Britain into submission (Shears 2001a p. 98). He launched Alderangriff (Eagle Attack start day) on 13 August but by 10 September, nearly a month later, the German naval staff noted that even the important Sea Lion precondition, “clear air command over the Channel, has not been achieved,” (Shears 2001a p. 99).

The Junkers Ju 88 (above) together with the Dornier DO 17, formed the backbone of Göring’s Operation Sea Lion bomber force.

It was the rugged Hawker Hurricane, not the much-vaunted Spitfire, that broke the back of the German bomber offensive.

Supplementing the Luftwaffe was the emplacement of heavy long-range guns on the French coast. These theoretically could protect substantial parts of the Sea Lion invasion fleet from British naval attacks and even destroy British beachhead targets.

The Germans established a battery of four 38 cm guns capable of hitting Dover, Hythe and Folkstone by about 1 August. They sited a number of other coastal batteries, giving a total of 29 guns, 38 cm to 17 cm in calibre, by the “middle of September” (Shields 2001b p. 106, Churchill p. 240). The British were slow to react with similar weapons, despite Churchillian prodding to create batteries, not only for cross-channel duelling, but also as anti-invasion weapons to interdict the beachheads. Even the old monitor Erebus, rail-mounted artillery and guns taken from refitting cruisers, such as Newcastle and Glasgow, were thrown into the plans to counter the German artillery threat.


Sea Lion postponed

In any event, whether by longstanding design or lessons learned from the invasion preparation failures, Hitler postponed Sea Lion twice, before postponing it indefinitely on 17 September. He then switched his total attention towards the Balkans and Soviet Union, including the buildup for the 22 June 1941 launch of Operation Barbarossa (Unternehemen Barbarossa). There is weak evidence to suggest that Hitler’s May-September Sea Lion vacillation was, in fact, linked to a grander strategy that used Sea Lion as a mere feint to hide his real purpose. If so, it was a costly feint, in terms of German aircraft lost and American support gained by the British.

Göring unwittingly assisted British strategy by an amazing failure to persist with his early aim of destroying all British radar sites and fighter airfields in southeast England. He also helped by persisting with Enigma, a complex cypher process read by the British.

Finally, while the British knew German dispositions and intentions fairly accurately, “German intelligence … was amateurish, to say the least,” (Shields 2001a p. 93).

Generally, German intelligence overestimated British ground strength in the critical invasion-scare months by eight divisions or so. They broke RN ciphers, but this advantage ended in August 1940, when the British became suspicious and changed their codes.

Amphibious operations, never simple, are heavily dependent on times and tides. A dawn assault guided by a half-to-full moon plus relatively storm-free seas gave the British relatively narrow high-alert time-frames to defend. British planners would agree with Raeder who recommended invasion either between 20 and 26 August 1940, which was too soon for his logistics preparations or 19 and 26 September, which was dangerously close to the October gale season.

Equipment shortages

In July 1940, after the May-June Dunkirk Operation Dynamo evacuation, the 27 British and Commonwealth divisions deployed in the UK were woefully under strength, particularly as far as weapons, transport and artillery were concerned. The Home Guard had few weapons and even fewer uniforms. Churchill reported the imminent arrival of American heavy weapons plus 100,000 rifles on 7 July and another 200,000 American rifles on 31 July (Churchill p. 237-238). By September, the British defenders were in reasonable shape, and getting stronger every day.

Churchill and Cox demonstrate that the British had excellent intelligence sources monitoring nearly every phase of the proposed invasion. They also emphasise that although Hitler considered Sea Lion as early as May 1940, he never seemed to give it his wholehearted support. Hitler was slow to give the plan his necessary full approval and he was fairly easily persuaded to defer the operation time and time again.

Above all, due in no small degree to poor interservice staff work, the German Navy could never meet the transport logistics timetable set by the German Army and, in any event, the failure of the German Air Force to achieve its strategic goals doomed the scheme to failure in utero.


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