Hitler postpones Operation Sea Lion

On 17 September 1940 Adolf Hitler decided to postpone “until further notice” Operation Sea Lion (Seelöwe), the planned landing in England. That day the war diary of the Naval War Staff recorded the reasoning: the enemy air force had not been defeated and, on the contrary, was showing ever greater activity, while the weather gave no grounds to expect a period of calm at sea; the Führer was therefore postponing the operation indefinitely. Under the timetable, this was the day on which the preliminary order for a landing on the last suitable date in September had to be given. It was not given. The condition on which Hitler had made the whole operation depend in July – the defeat of the British air force – had not been met.

War chronologies spread this story over four dates. Under 3 September they record that Hitler postponed the invasion because the Luftwaffe had failed to break the British defences; under 10 September, that Sea Lion was set for 24 September; under 14 September, that it was moved to 27 September, the last day of the month with a favourable tide; and under 17 September, that decrypted signals revealed the operation had been postponed indefinitely. These were successive steps in a single decision, and several of them need correcting. On 3 September the invasion was not postponed: rather, it was given a specific date for the first time, 21 September, and the reason earlier plans had slipped was the navy’s delay in its preparations, not any failure of the Luftwaffe. Nor were 24 and 27 September ever “set” as landing dates: they were the earliest possible dates, which followed from Hitler twice putting off the issue of the preliminary order. And on 17 September the British did not read in any signal that the operation had been postponed. They decrypted an order from which that could only be inferred.

The timetable of 3 September

Directive No. 17 of 1 August had ordered preparations for the landing to be completed by 15 September, with Hitler to decide on it after the first weeks of the intensified air war. Throughout August, however, the navy fell behind in converting river barges and moving them to the English Channel, and the dispute with the army over the width of the landing front dragged on until the end of the month. On 30 August the Naval War Staff reported that it could not complete its preparations before 21 September.

On 3 September the Chief of the High Command of the Wehrmacht (OKW), Field Marshal Wilhelm Keitel, issued an order fixing the timetable of the operation. The earliest day for the invasion fleet to sail was to be 20 September, and the earliest day for the landing (“S-Day”) 21 September. The navy needed ten days before sailing to sweep mines from the crossing routes and lay its own minefields on the flanks, so the order to begin the operation was to be given on “S-Day minus 10”, probably 11 September. Hitler was to give the final order no later than noon on the third day before the landing, and the whole undertaking had to remain capable of being called off up to twenty-four hours before zero hour.

The machinery was in motion. According to the British official history, by 4 September the Germans had requisitioned 168 transport ships with a combined tonnage of over 700,000 tons, 1,910 barges, 419 tugs and trawlers and about 1,600 motor boats – more than the Naval Staff had judged necessary six weeks earlier. The nine first-wave divisions of the 16th and 9th Armies held their assembly areas from Rotterdam to the area around Rouen. Near Calais and Boulogne stood heavy coastal batteries capable of shelling the English shore. Even so, there was plenty of doubt within the German command itself. General Kurt Student, creator of the German parachute troops who were to land in the first wave, recalled after the war that on 2 September he had heard the commander of the Luftwaffe, Reichsmarschall Hermann Göring, say: “The Führer does not want to go to England at all.”

Invasion on the doorstep

In Britain the first days of September brought the greatest fear of invasion since June. Aerial photographs of the coast from the island of Texel to Cherbourg showed barges moving westwards along canals and the shore. At Ostend there had been none on 28 August; there were 18 on 31 August and 270 on 7 September. Their numbers grew in the same way at Flushing (Vlissingen), Dunkirk and Calais. At the turn of August and September four German agents came ashore by boat on the coast of Kent. Caught within a few hours, they admitted that they were to be ready, within the next two weeks, to report on the movements of British reserves between London, Oxford, Reading and Ipswich. Three of them were hanged in December.

On 7 September the British Joint Intelligence Committee warned the Chiefs of Staff that invasion might be imminent, since the moon and tides on the south-east coast favoured a landing on 8–10 September. That same afternoon the Luftwaffe attacked London in full strength for the first time, beginning the Blitz. At 8.07 p.m. General Headquarters Home Forces sent the code word “Cromwell”, meaning immediate readiness for action, to the commands in eastern and southern England. In some places Home Guard commanders had church bells rung – the signal of a German landing – and the night passed amid false reports of parachutists. The next day the Commander-in-Chief Home Forces, General Alan Brooke, ordered that the bells were to be rung only when someone had seen with his own eyes at least 25 parachutists.

Hitler himself stoked the tension. On 4 September at the Berlin Sportpalast, in the speech in which he announced reprisals for the British raids on Berlin, he mocked the English who kept asking why he had not yet come: “Calm down, calm down – he is coming!” On 11 September Winston Churchill said in a broadcast that the coming week had to be regarded as a very important period in British history, comparable with the days when the Spanish Armada was approaching the Channel, or the time when Nelson stood in the way of Napoleon’s Grand Army assembled at Boulogne. The Royal Navy brought its heavy ships closer: on 13 September the battleship Nelson and the battlecruiser Hood moved from Scapa Flow to Rosyth. At night it sent cruisers and destroyers off Calais, Boulogne and Ostend, although they found few targets there, as shipping was already avoiding the ports nearest to England.

The battle of the barges

The greatest damage to the German preparations was done by British bombers. In July and August Bomber Command had attacked mainly targets in Germany and airfields, since there was as yet nothing to bomb along the Channel. When the barges began to fill the ports at the start of September, they became the main target. From the night of 5/6 September they were attacked by Blenheim light bombers, and soon also by Hampdens, Fairey Battles, Wellingtons and Whitleys. According to the British official history, attacks on the invasion ports absorbed about three-quarters of Bomber Command’s entire effort in September and more than a thousand tons of bombs. On the night of 13/14 September, for the first time, all of the night bombers’ activity went to the ports and shipping, and the following night the number of sorties nearly doubled.

On the night of 14/15 September the Polish bomber squadrons entered the fight. Three crews each from Nos. 300 and 301 Squadrons, flying Fairey Battles, bombed barges at Boulogne, and on the following nights they attacked Calais, Ostend and Dunkirk. On the night of 15/16 September a Hampden of No. 83 Squadron was hit and caught fire over Antwerp. Its eighteen-year-old wireless operator and air gunner, Sergeant John Hannah, fought the fire with extinguishers and then with his bare hands, and helped the pilot bring the aircraft back to base. For this he received the Victoria Cross, one of the youngest airmen ever awarded it. On 17 September 84 barges were sunk or damaged at Dunkirk.

The effects were felt. The roadsteads of the Channel ports ceased to be usable as night anchorages for transports, and the Naval Staff lost what optimism it had left. According to German figures that Churchill cited after the war, by 21 September 21 of the 170 transports and 214 of just under 1,920 barges had been destroyed or damaged – about 12 per cent of the tonnage. The attacks also showed that the RAF, which German intelligence described as close to exhaustion, still had strength for more than defence.

Postponement after postponement

What was decisive for Hitler, however, was the sky over England. From 7 September the Luftwaffe struck at London, hoping to force the last reserves of RAF fighters into battle and destroy them. When the date for the preliminary order arrived, Hitler did not issue it and put the decision off by three days, to 14 September. The British official history dates this decision to 11 September, some studies to 10 September. The postponement meant that the landing could take place on 24 September at the earliest; this is the origin of the date that chronologies give as the “set” date of the invasion. On 13 September Grand Admiral Erich Raeder reported to Hitler that Göring’s efforts had so far not created the conditions for carrying out the operation. The Naval Staff, which had received no help from the Luftwaffe against the British fleet, believed that minefields alone would not shield the crossing from the Royal Navy.

On 14 September Hitler assembled his commanders at the Reich Chancellery in Berlin. Present were Raeder, the Commander-in-Chief of the Army, Field Marshal Walther von Brauchitsch, the Chief of the General Staff, General Franz Halder, and, representing the Luftwaffe, Field Marshal Erhard Milch, since Göring was directing the raids from France. According to Halder’s notes and the navy’s minutes, Hitler praised the preparations and said that a successful landing would be the quickest way to end the war. He judged that the Luftwaffe had achieved a great deal but had not yet won air superiority, although four or five days of good weather might bring a decision. He did not want to cancel the operation, because that would bring the British relief, while the mere threat of a landing tied down their forces. The raids were to continue. A request from the Luftwaffe Chief of Staff, General Hans Jeschonnek, for permission to bomb residential districts in order to cause mass panic was rejected by Hitler, who kept such “terror” in reserve as a last resort. He put off the decision on the landing by a further three days, to 17 September. The landing could therefore take place on 27 September at the earliest, and that was the last day on which moon and tide favoured the crossing. The next suitable period would not begin until 8 October.

On 16 September Göring issued orders for a new phase of the raids, but the day before the Luftwaffe had suffered a defeat that many participants in the battle regarded as its turning point. On 15 September two great daylight raids on London were broken up by the fighters of No. 11 and No. 12 Groups, and German airmen, who had been told for weeks that the RAF was down to its last fighters, saw several hundred Spitfires and Hurricanes over the English capital. The Germans lost about 60 aircraft that day. On 15 September Raeder still regarded the landing as a desperate gamble, and the weather forecasts offered no hope of a longer spell of calm in the Channel.

The decision of 17 September

On 17 September, when the time came for the preliminary order, the Naval Staff favoured waiting and British resistance in the air was not weakening. Hitler postponed Sea Lion indefinitely. He stipulated that the possibility of a landing in October must be kept in mind, but at the same time agreed that the invasion fleet should be partly dispersed so that RAF bombers could not go on destroying it. The OKW issued orders to this effect over the following days. As early as 20 September British air reconnaissance found that six destroyers and a torpedo boat photographed in Cherbourg two days earlier had left the port (they soon appeared at Brest), and the number of barges visible in the five main ports from Flushing to Boulogne fell from 1,004 on 18 September to 691 in the last week of the month.

News of the decision reached London by another route. At Bletchley Park British codebreakers were by then reading some Luftwaffe signals enciphered on the Enigma machine – what later came to be called “Ultra”. According to F. H. Hinsley’s official history of British intelligence, on 17 September a signal was read reporting that the Führer had authorised the dismantling of the equipment for loading transport aircraft at airfields in the Netherlands. This equipment was needed to carry the airborne troops of the first wave. The signal did not speak directly of postponing the operation, but in London it was read as a clear sign that the immediate danger of invasion was passing. The often-repeated mention of “decrypted signals that revealed” the postponement should therefore be understood as an inference the British drew from an indirect clue, not as a reading of the decision itself.

A fear that did not pass

The British could not know, however, whether the postponement was final, and they did not relax their defences. Aerial photographs from the end of September and from October caused confusion: barges were becoming fewer, but the pictures showed ramps for rapid loading and strange pairs of barges joined together, and building work was under way at airfields in the Netherlands. Some of the barges had not gone far but had merely hidden in nearby canals, from which they could quickly return. Intelligence wondered whether the Germans were quietly preparing a landing from the Baltic ports, which reconnaissance aircraft could not photograph for a long time. Only at the end of October did the British command conclude that an expedition from the Channel ports was no longer imminent.

Among the public, meanwhile, rumours circulated that the Germans had already tried to land and had been driven off with heavy losses – and in some versions that the British had set the sea on fire by pouring oil onto it. The rumours were fed by the bodies of several dozen German soldiers washed up on English shores: victims of the bombing of the ports and of exercises with barges that had sunk in bad weather. The British government officially denied the rumours, but they did nothing to hinder its efforts to sustain the spirit of resistance at home and abroad.

Place in the war

In practice the decision of 17 September ended the invasion plans for 1940. The dispersed fleet could not be reassembled in time, and the autumn gales closed the Channel. On 12 October Hitler deferred the operation to the spring of 1941 and ordered that preparations should continue only as a means of political and military pressure on Britain. The barges began to be returned to inland shipping, and in January 1941 all work was stopped except the development of special equipment and deception measures. The Luftwaffe kept up its daylight raids until the end of October and its night offensive against British cities until May 1941, but the purpose of that offensive was now different: it was meant to break British industry and morale, not to prepare a landing. As early as September Raeder had urged Hitler to strike at the British in the Mediterranean, at Gibraltar and at the Suez Canal. Hitler, however, chose the east: on 18 December 1940 he signed Directive No. 21 for the attack on the Soviet Union, and from then on Sea Lion served mainly as a screen for those preparations.

The postponement of the landing was the most important result of the Battle of Britain. The airmen of Fighter Command, the sailors who guarded the Channel and the bomber crews who attacked the ports at night did not defeat the Wehrmacht, but they deprived it of its only chance of ending the war in the west quickly. Historians still argue over whether Hitler really wanted to land in England or whether the threat of a landing was meant above all to push London into negotiations. What is certain is that Britain, which he had managed neither to intimidate nor to conquer, survived the autumn of 1940 and stayed in the war, and in time became the base for the Allied bombing offensive and the landing in Normandy.