'Seelöwe' was the German unrealised plan for a combined-arms invasion of the UK (16 July/November 1940).

As early as the winter of 1939/40 Grossadmiral Erich Raeder, commander-in-chief of the German navy, had foreseen the need for an invasion if the UK refused to capitulate after the defeat of France, and ordered the preparation of preliminary plans. Raeder appreciated that the German army would regard any such invasion as little more than the assault crossing of a larger-than-average river, whereas he knew that such a crossing could face highly adverse weather and sea conditions, might face determined attack by the RAF, and would certainly encounter the full strength of the formidable Royal Navy even after the necessary operational pre-condition (Luftwaffe elimination of the RAF as an effective fighting force) had been achieved.

Raeder presented his initial ideas to Adolf Hitler on 21 May, but the German leader was at that time preoccupied with the course of operations in France and paid little attention. Thus it was only after the signature of the French armistice on 22 June, to come into effect on 25 June, that Hitler began to devote his full energies to the question of the UK, and three days after receiving an initial assessment prepared by General Alfred Jodl, chief-of-staff of the Oberkommando der Wehrmacht, on 2 July Hitler ordered preliminary planning, this being extended on 16 July by the Führerweisung Nr 16, which laid out the objectives of what had now become 'Seelöwe'. According to the directive, 'The aim of this operation is the elimination of the British homeland as a base for the further prosecution of the war against Germany, and, if necessary, to occupy it completely.'

Yet Hitler was still convinced that he could reach an accommodation with the British, and so delayed the start of full-scale preparations until he had made a 'last appeal to reason' in a speech on 19 July. On 22 July the British refused even to consider the German offer, so Hitler ordered that 'Seelöwe' be prepared for implementation in mid-September, while Reichsmarschall Hermann Göring’s Luftwaffe set about the destruction of the RAF as an essential precondition of the invasion. The German army had little experience even with the planning of an amphibious operation at the scale envisaged, but set about its task with the usual methodical professionalism, even if lack of understanding of the realities of amphibious warfare was evident, under the direct supervision of Generalfeldmarschall Walther von Brauchitsch and Generaloberst Franz Halder, the commander-in-chief of the army and chief-of-staff of the Oberkommando des Heeres respectively.

The initial German scheme was delivered to Hitler on 13 July, three days before the issue of Führerweisung Nr 16, and was built around the use of combat-experienced divisions (with supporting elements) of Generalfeldmarschall Gerd von Rundstedt’s Heeresgruppe 'A' and Generalfeldmarschall Fedor von Bock’s Heeresgruppe 'B' based in the north-east and north-west of France respectively. The army plan called for the initial assault wave of 11 infantry and two mountain divisions to be transported across the English Channel to secure (over a period of three days) a number of relatively small and unconnected beach-heads between Ramsgate and Lyme Bay. This scheme envisaged that six divisions of Heeresgruppe 'A' (the three corps of Generaloberst Ernst Busch’s 16^th Army) would be lifted from Rotterdam, Vlissingen (Flushing), Ostend, Nieuport, Dunkirk, Calais and Boulogne to be landed between Ramsgate and Bexhill, four divisions of Heeresgruppe 'A' (the two corps of Generaloberst Adolf Strauss’s 9^th Army) would be lifted from Le Havre to be landed between Brighton and the Isle of Wight, and three divisions of Heeresgruppe 'B' (one corps of Generalfeldmarschall Walther von Reichenau’s 6^th Army) would be lifted from Cherbourg to be landed in Lyme Bay.

These 13 assault divisions would be delivered in two waves (the first comprising 90,000 men, 650 tanks and 4,500 horses, and the second 160,000 men, 60,000 horses, between 30,000 and 40,000 vehicles, and 500 pieces of artillery), and would then be supplemented by 28 more divisions for the exploitation phase of the undertaking. This reinforcement would be delivered in three waves, the first consisting of six Panzer and three motorised infantry divisions in three corps plus Generalleutnant Kurt Student’s 7^th Fliegerdivision and Generalleutnant Hans Graf von Sponeck’s 22^nd Luftlande-Division in one Luftwaffe corps, the second of nine infantry divisions, and the third of eight infantry divisions.

The object of the assault by the divisions of Heeresgruppe 'A' was to secure a consolidated beach-head up to 20 miles (32 km) deep between Ramsgate and Bognor Regis, after which the Germans would advance to their first objective, a line stretching from Gravesend to Southampton and giving the Germans a secure lodgement in most of south-eastern England. With the arrival of the 28 reinforcement divisions, the formations of Heeresgruppe 'A' would sweep forward to their second objective, a line running from Maldon on the east coast to Gloucester on the Severn river, via St Albans and Oxford. The conurbation of London would not be assaulted in this phase, but cut off for subsequent reduction if the British failed to capitulate.

At the same time the divisions of Heeresgruppe 'B' in Lyme Bay would break out of their beach-head to secure south-western England before joining Heeresgruppe 'A' for an advance to the north, which was expected to reduce the rest of the UK in about one month.

The paradox of the German situation during July 1940 was the German navy, which had been the original sponsor of the 'Seelöwe' concept at a time when the army was wholly unenthusiastic, was becoming increasingly disenchanted with the notion even as the army’s enthusiasm grew. Raeder’s objections centred on the difficulty of undertaking the operation because of damage to the invasion ports caused by the implementation of 'Gelb' (in its 'Sichelschnitt' iteration) and 'Rot' (iii), the unpredictability of weather and sea conditions in the English Channel during the autumn season, Germany’s lack of adequate landing resources (requiring the collection and modification of coastal craft and barges from all parts of occupied Europe) and, perhaps most significantly, the inability of the German navy to secure the crossing lanes for the reinforcement divisions against the inevitable opposition of an undiminished Royal Navy. The naval arguments were compelling, and their meaning was not lost on the army, which was forced to scale down its plans to fit more closely the convoy and escort capacity offered by Raeder.

Even so, there remained a fundamental difference between the maximum that Raeder could offer and what the army saw as its minimum for a successful assault, so Hitler had to force a compromise on the two services at the end of August. The 6^th Army's landing in Lyme Bay was abandoned as an element of the assault phase, and the efforts of the 16^th Army and 9^th Army were scaled down. The 16^th Army was now to make two landings (one between Folkestone and New Romney, and the other between Camber and Hastings) to deliver General Heinrich-Gottfried von Vietinghoff-Scheel’s XIII Corps (Generalleutnant Herbert Loch’s 17^th Division, Generalleutnant Hans Wolfgang Reinhard’s 35^th Division and the Luftwaffe’s 2/14^th Flakregiment) and Generaloberst Eugen Ritter von Schobert’s VII Corps (Generalleutnant Ludwig Kübler’s 1^st Gebirgsdivision, Generalleutnant Eccard Freiherr von Gablenz’s 7^th Division and the Luftwaffe’s 1/26^th Flakregiment), while the 9^th Army was to make another two landings (one between Hastings and Eastbourne, and the other between Beachy Head and Brighton) to deliver General Erich von Manstein’s XXVIII Corps (Generalleutnant Sigismund von Forster’s 26^th Division and Generalleutnant Werner Sanne’s 34^th Division) and General Walter Heitz’s VII Corps (Generalmajor Ferdinand Schörner’s 6^th Gebirgsdivision, Generalleutnant Rudolf Koch-Erpach’s 8^th Division and Generalleutnant Johann Sinnhuber’s 28^th Division). Generalmajor Richard Putzier’s 7^th Fliegerdivision was to make parachute landings for the capture of the high ground north-west of Dover.

The forward perimeter of the initial beach-head was defined as a line from the middle of East Kent to Brighton, giving the Germans a lodgement some 15 miles (24 km) deep into which the second wave could be delivered for an exploitation to secure a line from the estuary of the Thames river via the North Downs to Portsmouth. Thus a first wave of seven infantry, two mountain and one parachute divisions would receive a second wave of four Panzer, two motorised infantry and two infantry divisions reinforced by two motorised regiments (for the 16^th Army General Richard Ruoff’s V Corps with Generalmajor Walter von Seydlitz-Kurzbach’s 12^th Division and Generalleutnant Kurt von Briesen’s 30^th Division, and General Georg-Hans Reinhardt’s XXXI Corps [mot.] with Generalleutnant Adolf Kuntzen’s 8^th Panzerdivision, Generalleutnant Ferdinand Schaal’s 10^th Panzerdivision, Generalmajor Walter von Boltenstern’s 29^th Division [mot.], Oberst Wilhelm-Hunold von Stockhausen’s Infanterieregiment 'Grossdeutschland' [mot.] and SS-Standartenführer Josef Dietrich’s SS Regiment 'Leibstandarte Adolf Hitler' [mot.], and for the 9^th Army Generaloberst Hermann Hoth’s XV Corps [mot.] with Generalmajor Willibald Freiherr von Langermann und Erlenkamp’s 4^th Panzerdivision, Generalmajor Erwin Rommel’s 7^th Panzerdivision and Generalleutnant Mauritz von Wiktorin’s 20^th Division [mot.]), a third wave of six infantry divisions (for the 16^th Army General Viktor von Schwedler’s VI Corps with Generalmajor Hans von Tettau’s 24^th Division and Generalmajor Iwan Heunert’s 58^th Division, and General Walter Kuntze’s XXXII Corps with Generalleutnant Friedrich Materna’s 45^th Division and Generalmajor Josef Folttmann’s 164^th Division, and for the 9^th Army General Leo Freiherr Geyr von Schweppenburg’s XXIV Corps with Generalleutnant Ernst-Eberhard Hell’s 15^th Division and Generalleutnant Curt Gallenkamp’s 78^th Division) plus an air-landing division if required, and an unspecified fourth wave.

If circumstances demanded and shipping permitted, the 6^th Army would be moved into the west country at the time the third and fourth waves of the 16^th Army and 9^th Army were delivered. On 6 September the 6^th Army came under the command of Generalfeldmarschall Wilhelm Ritter von Leeb’s Heeresgruppe 'C', which replaced Heeresgruppe 'B' on that date, and added to the German side of the equation Generalfeldmarschall Walther von Reichenau’s 6^th Army in the form of General Walter Graf von Brockdorff-Ahlefeldt’s II Corps with Generalleutnant Arnold Freiherr von Biegeleben’s 6^th Division and Generalmajor Gerhard Kauffmann’s 256^th Division.

Air support for the 16^th Army was to be provided by Generalfeldmarschall Albert Kesselring’s Luftflotte II, comprising the dive-bombers and attack aircraft of General Wolfram Freiherr von Richthofen’s VIII Fliegerkorps, the level bombers of General Bruno Lörzer’s II Fliegerkorps, the bombers and minelaying aircraft of Generalleutnant Joachim Cöler’s 9^th Fliegerdivision, the fighters of Generalmajor Theo Osterkamp’s Jagdfliegerführer 1 command, and the fighters of Generalmajor Kurt-Bertram von Döring’s Jagdfliegerführer 2 command. Air support for the 9^th Army was to be provided by Generalfeldmarschall Hugo Sperrle’s Luftflotte III, comprising the level bombers and dive-bombers of Generaloberst Ulrich Grauert’s I Fliegerkorps, the level bombers of Generalleutnant Kurt Pflugbeil’s IV Fliegerkorps, the level bombers of General Robert Ritter von Greim’s V Fliegerkorps, and the fighters of Oberst Werner Junck’s Jagdfliegerführer 3 command.

Under Raeder’s overall direction, control of the German naval operations of 'Seelöwe' was the responsibility of Generaladmiral Alfred Saalwächter’s Marinegruppenkommando 'West', which would therefore be responsible for operational direction of the light naval forces based in France and the Low Countries. The Seebefehlshaber 'West' for 'Seelöwe', and also the fleet commander, was Admiral Günther Lütjens, who would therefore be responsible for the tactical control and protection of the four transport fleets. The Kriegsmarine began assembling the following formations for protection of the convoy routes: two destroyer flotillas at Le Havre and four torpedo boat flotillas at Cherbourg to protect the western flank and three motor torpedo boat flotillas at Zeebrugge, Vlissingen and Rotterdam to protect the eastern flank. Also, 27 U-boats under the direction of Vizeadmiral Karl Dönitz were arranged to reinforce the convoy protection formations. Finally, nine patrol flotillas, 10 minesweeping flotillas and five motor minesweeping flotillas would accompany the transport convoys during the crossing of the English Channel. An additional three minesweeping flotillas, two anti-submarine flotillas and 14 minelayers were allocated to Marinegruppenkommando 'West' for supplementary support. Other German naval commanders involved in 'Seelöwe' were the Führer der Zerstörer (also commander of the 6^th Zerstörer-Flottille), namely Kapitän Erich Bey; and the Führer der Torpedoboote, namely Kapitän Hans Bütrow.

Based at Dunkirk, Transportflotte 'B' was commanded by Vizeadmiral Hermann von Fischel for the delivery of the first echelons of the 17^th Division and 35^th Division and the staff and corps troops, including Panzerabteilung B and Panzerabteilung D (less one company from the latter), of the XIII Corps. Subordinate commands were Tow Formation 1 at Dunkirk also under von Fischel, Tow Formation 2 at Ostend under Kapitän Walter Hennecke, Convoy 1 at Ostend under Kapitän Wagner, and Convoy 2 at Rotterdam under Kapitän Ernst Schirlitz. Based at Calais, Transportflotte 'C' was commanded by Kapitän Gustav Kleikamp for the delivery of the first echelons of the 1^st Gebirgsdivision and 7^th Division and the staff and corps troops, including Panzerabteilung A, of the VII Corps. It sole subordinate command was Convoy 3 at Antwerp under Kapitän Wesemann. Based at Boulogne, Transportflotte 'D' was commanded by Kapitän Werner Lindenau for the delivery of the first echelons of the 26^th Division and 34^th Division and the staff and corps troops, including Panzerabteilung C, of the XXXVIII Corps. Based at Le Havre, Transportflotte 'E' was commanded by Kapitän Ernst Scheurlen for the delivery of the first echelons of the 6^th Gebirgsdivision, 8^th Division and 28^th Division and the staff and corps troops, including one company from Panzerabteilung D, of the VIII Corps and X Corps.

Subordinate commands were Echelon 1a (originally Convoy 4) at Le Havre under Korvettenkapitän von Jagow, and Echelon 1b (originally Convoy 5) at Le Havre under Kapitän Ulrich Brocksien.

The German navy did not plan to make use of its few remaining heavy surface warships in the coastal waters of the main invasion area, but instead for diversionary operations designed to draw British naval forces away from the English Channel and tie down British troops away from the landing zones. Two days before the 'Seelöwe' landings, the light cruisers Emden (Kapitän Hans Mirow), Nürnberg (Kapitän Leo Kreisch with Vizeadmiral Hubert Schmundt, the Befehlshaber der Kreuzer, on board) and Köln (Kapitän Ernst Kratzenberg), the gunnery training ship Bremse and other light naval forces would escort the liners Europa, Bremen, Gneisenau and Potsdam, together with 11 transport vessels, on 'Herbstreise', a feint simulating a landing on the English east coast between Aberdeen and Newcastle. After turning about, the force would attempt the diversion again on the next day if necessary. (Most of the troops allocated to the diversion would actually board the ships, but disembark before the naval force sortied.)

Shortly before the start of 'Seelöwe', the heavy cruiser Admiral Hipper (on standby at Kiel from 13 September 1940) would carry out a diversionary sortie in the vicinity of Iceland and the Færoe islands group, and the pocket battleship Admiral Scheer would carry out another diversionary mission by raiding merchant shipping in the Atlantic, although it is doubtful that the ship would actually have been available as she was undergoing extensive trials and crew training in the Baltic Sea in the aftermath of a major refit. The remaining German heavy surface warships, namely the battle-cruisers Scharnhorst and Gneisenau, heavy cruiser Lützow and light cruiser Leipzig (decommissioned) were all undergoing repairs for varying degrees of battle damage and were thus not available for 'Seelöwe'.

In August 1940, the Kriegsmarine considered employing the pre-dreadnought battleships Schleswig-Holstein and Schlesien to provide gunfire support for the landings, but ultimately rejected the idea.

The army was still unhappy with this revised plan, which promised landings on a front that the army planners believed to be too narrow, but Raeder was adamant that this was the best that his resources would permit.

At this time the British defence was adequately organised on paper, but still suffering from the catastrophes of France and the Dunkirk evacuation, and also disastrously short of trained men and weapons, especially artillery and armour. Under the overall control of the War Office in London, where General Sir Alan Brooke was the commander of the UK Home Forces, the defence of the most threatened sector in south-eastern England was entrusted to Lieutenant General A. F. A. N. Thorne’s XII Corps (Kent, Sussex and Surrey), which controlled Major General C. F. Liardet’s 1^st Division, Major General E. C. A Schreiber’s 45^th Division and Major General B. C. Freyberg’s New Zealand Division, Brigadier Sir Oliver Leese’s 29^th Independent Brigade Group and Brigadier M. B. Burrows’s 1^st Motor Machine Gun Brigade. To the west of the XII Corps was Lieutenant General B. L. Montgomery’s V Corps (Hampshire, Wiltshire, Somerset and Dorset), which controlled Major General J. A. H. Gammell’s 3^rd Division, Major General T. R. Eastwood’s 4^th Division and Major General G. Le Q. Martel’s 50^th Division, the Australian Infantry Force, Brigadier G. P. L. Drake-Brockman’s 21^st Army Tank Brigade and one brigade of Major General J. C. Tilly’s 2^nd Armoured Division. Still farther to the west was Major General H. E. Franklyn’s VIII Corps (Devon and Cornwall), which controlled Major General R. L. Petre’s 48^th Division and Brigadier P. Kirkup’s 70^th Independent Brigade Group. East Anglia was the responsibility of Major General E. A. Osborne’s II Corps and Major General H. R. S. Massy’s XI Corps, which between them controlled Major General R. Le Fanu’s 15^th Division, Major General B. C. T. Paget’s 18^th Division, Major General J. S. Drew’s 52^nd Division and Major General V. H. B. Majendie’s 55^th Division, and Brigadier R. J. P. Wyatt’s 37^th Independent Brigade Group.

In reserve for these most threatened sectors were the two corps of the GHQ Reserve, namely Major General A. G. L. McNaughton’s VII Corps (Surrey and Berkshire) with Major General R. Evans’s 1^st Armoured Division, Major General G. R. Pearkes’s Canadian 1^st Division and Brigadier H. R. B. Watkins’s 1^st Army Tank Brigade, and Lieutenant General F. P. Nosworthy’s IV Corps (north of London) with Tilly’s 2^nd Armoured Division (less the brigade in the west country), Major General H. B. B. Willcox’s 42^nd Division, Major General R. V. Pollock’s 43^rd Division, and one independent infantry brigade group. London was defended by three infantry brigades, the East Midlands and north-eastern England by Major General the Hon. Sir Harold Alexander’s I Corps and Lieutenant General W. G. Holmes’s X Corps (five infantry divisions and one army tank brigade), the West Midlands, Wales and the north-western England by Lieutenant General Sir James Marshall-Cornwall’s III Corps (two infantry divisions, one infantry brigade, one motor machine gun brigade and one army tank brigade), Scotland by Lieutenant General Sir George Collingwood’s Scottish Command with three infantry divisions and one motor machine gun brigade, and Northern Ireland by Major General R. P. Pakenham-Walsh’s Northern Ireland District with two infantry divisions and one infantry brigade.

Frantic German preparations continued throughout late July and August, but were much hampered by the activities of British bombers and the gunfire bombardments of British warships, which had as their primary target the ports in which the invasion transport force was being gathered and modified, but on 11 September Hitler announced that the countdown for 'Seelöwe' would begin on 14 September for a landing at dawn on 24 September. On 14 September Hitler postponed his decision for three more days, however, and on 17 September he postponed 'Seelöwe' indefinitely because the Luftwaffe had manifestly failed to subdue the RAF in the Battle of Britain. Hitler ordered that the invasion fleet be returned to normal service, but only in such a way that it could be rapidly reassembled for a revival of 'Seelöwe' in the spring or summer of 1941.

In March 1942, with his forces deeply committed in the USSR, Hitler ordered that 'Seelöwe' be put on one-year notice, and the scheme was effectively forgotten.