below The unexpected collapse of France in May/June 1940 turned the theoretical risk of a German invasion of Britain into a real threat.

They’re coming! The invasion scares of 1803-05 & 1940

Napoleon and Hitler both drew up detailed plans for the invasion of Britain, spreading alarm among the public and forcing urgent measures from the UK government in return. Here, David Porter compares the plans, and the threat posed by the country’s two would-be invaders.


On 4 June 1940, as the last British and other Allied forces were evacuated from the beaches of Dunkirk, Winston Churchill gave what would become one of the best-known speeches of the 20th century. Addressing the House of Commons, the newly installed prime minister warned of the sacrifice that would likely soon be needed to deter the imminent threat of invasion by the most powerful armed forces ever assembled.

‘Even though large tracts of Europe and many old and famous States have fallen or may fall into the grip of the Gestapo and all the odious apparatus of Nazi rule, we shall not flag or fail,’ he said defiantly. ‘We shall go on to the end. We shall fight in France, we shall fight on the seas and oceans, we shall fight with growing confidence and growing strength in the air, we shall defend our island, whatever the cost may be. We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender…’ (As he sat down, he supposedly quietly remarked to a fellow MP: ‘And we’ll fight them with the butt ends of broken beer bottles because that’s bloody well all we’ve got!’)

The unexpected collapse of France in May/June 1940 turned the theoretical risk of a German invasion of Britain into a real threat. Image: Alamy.

It wasn’t the first time, of course, that Britain had faced invasion. With his unique ‘feel’ for history, Churchill was well aware of earlier ‘scares’ – especially those of the Napoleonic Wars, which in many respects paralleled that of 1940. As a new film opens in cinemas depicting Napoleon’s meteoric rise to power, we compare the two crises, which could so easily have ended in actual invasions. After all, as Churchill said in 1948, ‘Those who fail to learn from history are condemned to repeat it.’

The French menace: 1803-05

By the time of the Napoleonic Wars, the invasion of Britain had become a well-established feature of French military planning. Between 1700 and the outbreak of the Revolution of 1789, there had been at least nine such projected invasions, and the concept appealed strongly to Napoleon’s soaring ambitions. He was especially inspired by the successful landing of a tiny French force in Ireland in support of the 1798 rebellion, demonstrating that an invasion could avoid interception at sea.

Following a brief suspension of hostilities during the Peace of Amiens (March 1802 to May 1803), Napoleon assembled a 200,000-strong force deployed in camps at Boulogne, Bruges and Montreuil, known as the Armée des côtes de l’Océan (Army of the Ocean Coasts) or the Armée d’Angleterre (Army of England). A Flottille de Boulogne (Flotilla of Boulogne) of roughly 2,000 invasion craft was built in the Channel ports and concentrated at Boulogne. Almost half the force comprised gunboats of various sizes, plus 765 armed transports and about 350 converted fishing boats and coasters. The largest vessels were prames armed with 24-pounder guns and carrying up to 150 men; the second and most numerous were the péniches, armed with howitzers and capable of transporting 55 men; while the chaloupes cannonières were armed with howitzers and were supported by smaller gunboats. All were shallow-draught vessels fitted with specially designed ramps to allow an assault force of 149,000 men with artillery and 8,600 horses to disembark across beaches. (However unseaworthy they may have been, the invasion fleet was seen as enough of a threat to justify a series of raids, including a major operation against Boulogne in October 1804, which achieved little apart from prompting the French to improve their coastal defences.)

Following the Peace of Amiens (1802-03), Napoleon assembled a 200,000-strong force in camps at Boulogne, Bruges and Montreuil. Image: Wikimedia Commons
Napoleon’s review of his forces at Boulogne, 15 August 1804. Image: Wikimedia Commons

Napoleon never fully appreciated the differences between naval and land warfare, and persisted in treating the invasion as little more than an opposed river-crossing. He habitually overruled his admirals when they attempted to explain the realities of coping with the Channel’s tides, shoals and unpredictable weather. In the summer of 1804, he ordered a review of the invasion fleet despite Admiral Bruix’s warnings of a storm, which broke just as the review was about to begin, wrecking scores of gunboats and costing the lives of at least 200 men. Despite this vivid illustration of the problems of handling the mass of barely seaworthy invasion craft, which would take days to put to sea and cross the Channel, he continued to devise a series of ingenious plans that largely ignored the naval practicalities of the era.

On the resumption of war in 1803, the British government renewed many of the anti-invasion measures of the 1790s – the most important of which was the deployment of the Royal Navy’s Western Squadron, tasked with blockading the French Channel ports and defeating any invasion at sea. It was supported by the Sea Fencibles, a volunteer force established in the 1790s and reinvigorated in 1803. Their duties encompassed the manning of coastal defences (including floating artillery batteries and Martello towers) and crewing small coastal vessels. By the end of 1803, their numbers peaked at 25,000, but they still boasted a headcount of 23,000 when they were disbanded in 1810.

An imaginative view of Napoleon’s planned invasion shows a French force advancing through a Channel tunnel, while French balloons fight British man-lifting kites. Image: Alamy.
A print by James Gillray ridicules the idea of a French invasion, showing Napoleon and a rabble of French troops fleeing from British artillery fire. Image: Wikimedia Commons

The British recognised that there was no guarantee a French landing could be prevented, and the regular army establishment was increased to 132,000 men, of which 70,000 were specifically earmarked for the defence of the United Kingdom (Ireland had become part of the Union in 1800), and more than 25,000 for the colonies. They were supported by the 30,000-strong Army of the Reserve, together with the Militia and Volunteers. By the end of 1803, a great upsurge of patriotic feeling had raised almost 615,000 men for home defence. However, training and equipping them was another matter, and as late as March 1804, only 213,000 Volunteers had been issued with muskets, leaving at least 120,000 armed with nothing better than pikes and pitchforks.

Patriotism was all very well, but a mass of poorly trained manpower was never going to stand a chance of defeating Napoleon’s veterans in open battle, and a frantic effort was made to fortify key sectors of the coastline. The commonest defences were Martello towers – stone artillery towers up to 40 feet (12m) high, each garrisoned by one officer and 25 men, and usually armed with a single 24- or 32-pounder cannon mounted on a traversing carriage. A total of 140 Martello towers were built around Britain, of which 74 formed a chain along the Kent and East Sussex coast between Folkestone and Seaford. This sector was reinforced by the Royal Military Canal, running for 28 miles (45km) between Seabrook, near Folkestone, and Cliff End, near Hastings, following the old cliff line bordering Romney Marsh.

In addition, two 11-gun circular forts were built at Eastbourne and Dymchurch, together with a major fortress complex on the Western Heights above Dover. Work on the Dover fort began in 1804 (although the idea had been approved and funded as early as 1779) and consisted of three independent structures: the citadel, the Drop Redoubt and the Grand Shaft. The citadel was a large fort with bastions and ditches, which still had not been completed by the end of the Napoleonic Wars. The Drop Redoubt was a fortification close to the cliff edge, from which the defenders could counter-attack any landing force on the beaches using the triple staircase in the 180-foot-deep (55m) Grand Shaft. The Western Heights defences were intended to house 6,000 men and 139 guns, but they were never completed as the project was hugely expensive, and funding was withdrawn as soon as the threat of invasion passed.

Although the bulk of the Armée d’Angleterre (now called the Grande Armée) was redeployed to central Europe to counter the Austrian forces that invaded the French client state of Bavaria in September 1805, it was only Nelson’s victory at Trafalgar the following month that effectively ended the threat of a French invasion. But by then, the perceived menace had become deeply embedded in the British psyche, with Napoleon (‘Boney’) caricatured as a bogeyman. Well into the Victorian era, unruly children were warned: ‘Behave, or Boney will get you!’

The German threat: 1940

While the 1803-05 invasion scare was the culmination of a series of alerts dating back to the 1790s, that of 1940 was sudden and almost totally unforeseen. Although both British and German studies of a potential invasion of Britain had been carried out as early as 1939, these were little more than low-level contingency plans. It was only the unexpected collapse of France in May/June 1940 that turned a theoretical risk into a real threat. Fortunately for the British, no one in Germany had believed that France would be overrun so quickly, and it was not until early July that serious planning began for an invasion – later code named Seelöwe (Sea Lion).

A map showing plans for Operation Sea Lion reveals how Nazi Germany was preparing for an invasion of England across a wide section of the country’s south coast. Image: Alamy.

The invasion planning was marked by continual wrangling – the Heer (army) initially regarded the operation as ‘a river crossing on a broad front’, and insisted on landings on a 275-mile (443km) stretch of coastline from Ramsgate to Portland. The Kriegsmarine (navy) protested that anything more than an assault on a narrow front between Dover and Eastbourne would be impossible to protect from British naval units based at Plymouth and Portsmouth. This stance infuriated General Franz Halder, the chief of staff of the Army High Command (OKH), who noted: ‘I regard it as complete suicide, I might as well put the troops straight through a sausage machine.’

Above & below: The Germans planned to transport the bulk of their invasion forces in barges, such as these assembled at the port of Wilhelmshaven, as there were all too few proper landing craft like this Pionierlandungsboot. Image: Alamy
Trials of the prototype deep-wading Tauchpanzer III. Image: Alamy

The final compromise adopted on 30 August 1940 envisaged a first wave of nine divisions from the 9th and 16th Armies landing at four locations: two infantry divisions on beach ‘B’, between Folkestone and New Romney, supported by a company of the special forces Brandenburg Regiment; two infantry divisions on beach ‘C’, between Rye and Hastings, supported by three battalions of amphibious tanks; two infantry divisions on beach ‘D’, between Bexhill and Eastbourne, supported by another battalion of amphibious tanks and a second company of the Brandenburg Regiment; and three infantry divisions on beach ‘E’, between Beachy Head and Brighton.

An airborne division would land in Kent, north of Hythe, with the objective of seizing the airfield at Lympne and the bridges over the Royal Military Canal before assisting the ground forces in capturing Folkestone. Newhaven and Folkestone were the only ports within striking distance of the invasion forces, and much depended on these being captured substantially intact, or needing only rapid repair – in which case, the second wave of eight divisions, including all the motorised and armoured divisions, might be unloaded directly onto their quaysides. A further six infantry divisions were allocated to the third wave.

As there were very few purpose-built landing craft, the vast bulk of this force was to be carried in a motley collection of roughly 2,400 barges towed by hundreds of tugs – an armada just as unseaworthy as Napoleon’s invasion fleet. The majority of the barges were fitted with improvised bow ramps to allow troops to land on open beaches, although a small number were adapted to launch amphibious Panzer II tanks and the deep-wading Tauchpanzer III and IV. (The Tauchpanzers were adapted Panzer IIIs and IVs.) As with Napoleon’s invasion fleet, the British regarded the barges as a sufficient threat to justify a series of raids on the French Channel ports, and by 21 September claimed to have sunk 67 vessels and damaged a further 173.

The recent Norwegian campaign had crippled the Kriegsmarine, but it had cost the Royal Navy an aircraft carrier, two cruisers, seven destroyers and a submarine. While these losses had scarcely affected British naval superiority, they served as a warning that a combination of mines, E-boats, U-boats, coastal artillery and air attacks could inflict devastating losses on the Home Fleet if it were forced into the confined waters of the Channel to oppose an invasion. (The Germans laid a high proportion of their planned 12,000-plus mines: on 31 August, the Royal Navy’s 20th Destroyer Flotilla ran into a minefield off Texel, losing two destroyers. A light cruiser and another destroyer were damaged.)

If the naval balance of power favoured Britain, the Germans had a massive advantage on land – a total of 368,491 British troops had been evacuated from France, but there were more than 66,000 casualties, many of them pre-war regulars whose expertise made them hard to replace. In addition, vast amounts of stores and equipment were destroyed or abandoned, including 689 tanks, plus 2,472 guns, more than 75,000 tons of ammunition and 162,000 tons of fuel. German casualties in the Battle of France had been significant, at more than 157,000, but were still far fewer than expected, and little more than a third of those sustained during the 1916 Battle of Verdun. The victory provided an enormous boost to morale – one junior officer recalled how his men were ‘on top of the world, they felt that they could achieve anything’. By contrast, British army morale had been badly shaken (at least temporarily). There were reports of exhausted troops newly evacuated from France dumping their equipment with the comment: ‘What’s the point? They’ll probably be here next week.’

The 4 August 1940 edition of the Sunday Graphic newspaper warns of the continuing threat of a German invasion. Image: Wikimedia Commons

The defeat in France had left most British infantry divisions at about half-strength (roughly 7,000 men), with only around one-sixth of their normal artillery (12 rather than 72 field guns). The vital sector of coastline from Sheppey to Rye was manned by the 1st London Division, with no medium machine-guns or anti-tank guns, 23 field guns out of an establishment of 72, and no armoured fighting vehicles. As late as 13 September, General Sir Alan Brooke, who had succeeded General Sir Edmund Ironside as C-in-C Home Forces, noted that, of the 22 divisions under his command, ‘only about half can be looked upon as in any way fit for any form of mobile operations.’

The urgent need for some form of additional home defence force had prompted the formation of what were initially termed the Local Defence Volunteers (LDV) in May 1940. In many respects, these were the equivalent of the Napoleonic Militia and Volunteers, raised in an equally febrile atmosphere of patriotic enthusiasm. Just as in 1803-05, there were far too many men to be adequately armed and equipped – a total of 250,000 volunteers came forward in the first week, and after two months (when the force was renamed the Home Guard) this had risen to 1,500,000. Initially, the Home Guard was desperately short of weapons, as the regular army naturally took priority for whatever was available to replace the equipment lost in France; and even by September, many Home Guard units were virtually unarmed. A public appeal brought in 20,000 revolvers and shotguns, but many units were armed with an eclectic collection of shotguns, air rifles, old hunting rifles, museum pieces, and improvised ‘pikes’ – often lengths of pipe with knives or bayonets welded to the end. The weapons situation was improved by the delivery of US rifles, which began in mid July, although all ammunition had to be imported, as these weapons were chambered for American .3-inch ammunition and were initially supplied with only 10 rounds each.

A network of 28,000 pillboxes such as these, near Farnham, in Surrey (above) and overlooking the port of Dover (below)was built to prevent German invaders ‘running riot’. Images: Wikimedia Commons

The obvious limitations of the ‘post-Dunkirk’ army and Home Guard prompted the frantic construction of a staggering variety of fortifications. As early as 27 May 1940, a Home Defence Executive was formed under Ironside, which authorised the building of defences to form a ‘coastal crust’ and a series of inland anti-tank ‘stop’ lines. These defences comprised about 28,000 concrete pillboxes, plus anti-tank obstacles, trenches and minefields – as Ironside explained: ‘This system of stops and strong-points will prevent the enemy from running riot and tearing the guts out of the country as happened in France and Belgium.’ The final and main defence line was the General Headquarters Anti-Tank Line (the GHQ stop-line) covering Bristol, London and the major industrial centres of the Midlands and the North.

In many instances, Napoleonic-era defences were reused – the Royal Military Canal was reinforced with pillboxes and defended by 31st Independent Brigade Group. A large number of the surviving Martello towers were incorporated into the defences by adding observation posts and concrete machine-gun emplacements. In some cases, parts of even earlier fortifications were adapted, including the Roman ‘Saxon Shore’ fort at Pevensey.

It is arguable that command of the air was a decisive factor in 1940 – had Göring maintained the pressure on RAF Fighter Command’s 11 Group, the Luftwaffe might well have gained air superiority over the Channel and the ‘invasion coast’, dramatically improving Seelöwe’s chances of success. Although air attack was beyond the technology of 1805, Napoleon seriously considered using a fleet of troop-carrying balloons as part of his invasion force. (The first cross-Channel balloon flight, from Dover Castle to Guînes, had been made by Jean-Pierre Blanchard and John Jeffries on 7 January 1785.) However impractical, this idea captured the imagination of the British public, especially after the First Lord of the Admiralty, Lord St Vincent’s widely reported remark: ‘I do not say they [the French] cannot come – I only say they cannot come by sea.’

Although orthodox historians are now inclined to dismiss Napoleon’s and Hitler’s invasion plans as hopelessly impractical, one thing remains clear: they seemed all too feasible to their contemporaries. Perhaps we have allowed hindsight to distort our view?

The film Napoleon is released on 24 November, and will be reviewed in the next issue of MHM.

David Porter worked at the Ministry of Defence for 30 years, and is the author of 11 Second World War books, as well as numerous articles for MHM.