British anti - invasion preparations of 1803 – 1805 British anti - invasion preparations of 1803 – 1805 were the military and civilian responses in the United Kingdom to Napoleon ' s planned invasion of the United Kingdom . They included mobilisation of the population on a scale not previously attempted in Britain , with a combined military force of over 615 , 000 in December 1803 . Much of the southern English coast was fortified to repel a French landing . However Napoleon never attempted his planned invasion and so the preparations were never put to the test . Background . In the aftermath of the French Revolution of 1789 Britain and France were at war almost continuously from 1793 to 1802 , and then from 1803 to 1815 , interrupted by the brief Peace of Amiens of 1802 – 3 and Napoleon ' s first exile at Elba in 1814 – 15 . In late 1797 , Napoleon said to the French Directory that : [ France ] must destroy the English monarchy , or expect itself to be destroyed by these intriguing and enterprising islanders . . . Let us concentrate all our efforts on the navy and annihilate England . That done , Europe is at our feet . However Napoleon decided against invading for the time being and instead unsuccessfully attacked British interests in Egypt . In March 1802 the two countries signed the Treaty of Amiens , which brought to an end nearly nine years of war . However both the British Prime Minister Henry Addington and Napoleon viewed the peace as temporary , and so it was , with Britain declaring war on France on 18 May 1803 . William Pitt replaced Addington as Prime Minister on 10 May 1804 . In 1803 Napoleon turned his attention to invading England once more , saying : " All my thoughts are directed towards England . I want only for a favourable wind to plant the Imperial Eagle on the Tower of London " . Napoleon now planned an invasion on a bigger scale than 1798 and 1801 , and built a new armada for the effort . He assembled the Grande Armée of over 100 , 000 at Boulogne . British armed forces . Regular Army . Addington ' s government had kept the Regular army at 132 , 000 men during the Amiens interlude , with 18 , 000 in Ireland and 50 , 000 in Great Britain ( the rest serving abroad ) . Army of Reserve . In 1803 50 of the 93 regiments of the Army gained a second battalion , which became known as the Army of Reserve . These 50 , 000 men would be raised by ballot within one year . However each recruit was liable to serve in Great Britain only . These Reserve soldiers could volunteer as Regular soldiers and consequently receive money . After 9 months recruiting fewer than 3 , 000 of the 42 , 000 men were balloted men . Within one month of recruiting it had enlisted 22 , 500 men but by the end of 1803 it was short of the required 50 , 000 by 15 , 000 so the government stopped recruiting for it . Militia . The Militia was a territorial - based infantry to be used only for home defence and was not a standing army . It was to be raised by ballot . The government in December 1802 , fearing war , held a Militia ballot . The ballot was run by churchwardens and overseers of the poor in each parish . A list of men aged between eighteen and forty - five , with many exceptions ( such as seamen and Thames watermen ) , was posted on the front of the church door . However if a man found himself on the list he could get out of serving by paying a fine or getting another man to fill his place . Four months after the ballot , and a week into the war , the Militia was filled to 80 % of the 51 , 000 required . Volunteers . The British government had no choice — in view of Napoleon ' s avowed determination to invade the United Kingdom — but to rely on the patriotism of the people through a volunteer movement . The volunteers ' function , as laid down in July 1803 by the Commander - in - Chief of the Forces , Prince Frederick , Duke of York , was to conduct guerrilla warfare against the French occupying forces . They would operate in small bodies to harass , instill panic and wear out the French army . They were never to get deeply engaged with French troops and to retire when pressed . Local knowledge was to be used as much as possible and they were also expected to cut off French pillaging detachments . In anticipation to criticisms that arming the people was dangerous , the Secretary at War in Addington ' s government ( Charles Yorke ) said on 18 July 1803 in introducing a Bill for amending the Defence of the Realm Act : I say , that in these times , it is better to run the hazard even of the people making a bad use of their arms , than that they should be actually left in a state of entire ignorance of the use of them . For my own part , I can safely aver , that I cannot see any real danger which is likely to accrue to the internal peace of the Country , when I consider the present dispositions and feelings of the people . William Pitt , in response , agreed : I am sure there is not an heart that palpitates in a British bosom that will not rouse for the common cause , and cordially join for the defence of the country . . . . That there was a time , Sir , when it would have been dangerous to entrust arms with a great portion of the people of this country , I have strong reasons to know , because it must be in the recollection of every man that incendiaries were at work amongst them ; and so successful in the promulgation of revolutionary doctrines , as to have disposed them to exert any means , however desperate , which they thought could be successful , in subverting the Government and Constitution . But that time is now past ; and , I trust , those who have been so grosly deluded have seen their error . At least I am convinced , that if any such there still remain , the portion is so small , that if armed and dispersed in the same ranks with their loyal fellow subjects , they would be converted by their example ; and , like them , rejoice in the blessings of our happy constitution ; like them glory to live under its auspices , or die in its defence . Even the prominent anti - war MP Charles James Fox supported the Bill : This is the first measure which I could . . . come down to support , being a measure for the defence of the country . . . the mass of the country ; acting , not in single regiments , but as a great mass of armed citizens , fighting for the preservation of their country , their families , and every thing that is dear to them in life . . . an armed mass of the country , who are bound by every feeling and by every tie to defend that country to the last drop of their blood , before they will give way to him and his invading forces . During 1803 the government ' s call for volunteers to resist an invasion was met with a massive response . However the government was unprepared for the numbers of volunteers , as within a few weeks 280 , 000 men had volunteered . On 18 August Addington issued a circular discouraging new volunteers " in any county where the effective members of those corps , including the yeomanry , shall exceed the amount of six times the militia " . This had little effect since by the first week of September there were 350 , 000 volunteers . At least half of the volunteers of the summer and autumn of 1803 were not equipped with their own weapon . When the government tried to issue them with pike s this was met with contempt and attacked by the Opposition leader William Windham . The second half of 1803 marked the height of the invasion scare . When the King reviewed 27 , 000 volunteers in Hyde Park , London on 26 and 28 October 1803 , 500 , 000 people were estimated to have turned out on each of the two days to witness the event . The Chief Constable of Bramfield ( John Carrington ) travelled from Hertfordshire to see it , saying : " I never saw such a sight all my days " . These were the best - attended of reviews of volunteers which between 1797 and 1805 " were often of daily occurrence " . In 1804 returns to Parliament recorded a total of 480 , 000 volunteers in uniform . In addition there were the regular forces and the militia , which meant that nearly one - in - five able - bodied men were in uniform . The Speaker , addressing the King at the prorogation of Parliament on 13 August 1803 , said " the whole Nation has risen up in Arms " . Addington called the volunteer movement on 4 September 1803 " an insurrection of loyalty " . The response to the call to arms to resist invasion in these years has impressed some historians : " If some dissentient voices were heard in 1797 – 8 when the aftermath of the Revolution still lingered in the land , there was increased enthusiasm in the patriotism of 1801 , and burning ardour coupled with absolute unanimity in that of 1803 – 5 " . Royal Navy . The Royal Navy kept a constant blockade of French harbours from Toulon to the Texel , just outside artillery range , waiting for a French ship to sail close enough to be attacked . Rear - Admiral of the United Kingdom Admiral Cornwallis had a fleet off Brest and Commander - in - Chief of the North Sea Admiral Keith possessed a fleet between the Downs and Selsey Bill . A further line of British ships lay close to the English coast to intercept any French ships that broke through the blockade . The French were unwilling to venture out of their ports and so in the two years only nine flotilla ships had been captured or sunk by the Royal Navy . During the end of December 1803 a violent storm blew Cornwallis ' s fleet from Brest and it had to stay in Torbay , giving the French fleet two days opportunity to invade . Upon hearing this Addington gave orders to prepare for an imminent invasion , but the French never used this opportunity . First Lord of the Admiralty Lord St . Vincent is said to have told the House of Lords : " I do not say the French cannot come , I only say they cannot come by sea " . A volunteer force called the Sea Fencibles had been formed in 1793 ; they manned small armed boats , watch and signal towers , and fixed and floating batteries along the coasts . Fortifications . In July 1803 the Duke of York argued for the construction of field fortifications as soon as possible because " the Erection of such Works must be immediate with a view to their probable utility " , placing them at " Points where a Landing threatens the most important interests of the Country " . In August he requested from Addington further funds for such fortifications , who eventually consented . The Duke of York ' s priorities were the building of considerable fortifications at the Western Heights looking over the port of Dover and then the construction of Martello towers along the Kent and Sussex coasts . Martello towers . Across the coast of Kent and Sussex the government constructed a series of well - fortified towers , known as Martello tower s , between 1805 and 1808 . In September 1804 Pitt ' s government ordered General Sir William Twiss to scout the south - east coast of England for possible sites for Martello towers , to be used as artillery emplacements . Twiss earmarked eighty - eight appropriate sites between Seaford and Eastwear Bay . Twiss also headed the team that designed the Martello towers . Twiss ' s plan was adopted in October at a defence conference in Rochester attended by Pitt , Lord Camden , the Duke of York , Lord Chatham , Major General Sir Robert Brownrigg , Lieutenant Colonel John Brown and Twiss . Eventually seventy - four towers were built , with two ( Eastbourne and Dymchurch ) being considerably larger with eleven guns and housing 350 soldiers . These became known as Grand Redoubt s . A second line of twenty - nine towers , from Clacton - on - Sea to Slaghden near Aldeburgh , was constructed by 1812 , including a redoubt at Harwich . Forty were built in Ireland . Royal Military Canal . During the summer of 1804 , Lieutenant Colonel Brown was sent to examine the coast to discover if flooding of Romney Marsh would be viable in case of invasion . Brown thought it would not be and believed security would be improved by the excavation of " a cut from Shorncliffe battery , passing in front of Hythe under Lympne heights to West Hythe . . . being everywhere within musket shot of the heights " . Brown then advocated an extension of the water barrier : " . . . cutting off Romney Marsh from the county , opening a short and easy communication between Kent and Sussex but , above all , rendering unnecessary the doubtful and destructive measure of laying so large a portion of the country waste by inundation " . This became known as the Royal Military Canal , with construction starting in 1805 and completion in 1810 . Western Heights . General Twiss recommended a fortress at Dover , with work beginning in 1804 . The Western Heights at Dover consisted of three parts : the Drop Redoubt , the Citadel and the Grand Shaft . The Drop Redoubt was a detached fort close to the steep cliffs , surrounded by ditches and intended for soldiers to go out and attack French infantry , built between 1804 and 1808 . The Citadel was a larger fort surrounded by ditches and was still unfinished when war with France ended in 1815 . The Grand Shaft was a barracks containing sixty officers and 1300 NCOs and soldiers , begun in 1806 and completed in 1809 . Telegraphs . In order for the government to better communicate with the coast in case of invasion , a system of telegraphs was constructed . In January 1796 , a telegraph line from the Admiralty in London to Deal , Kent had been built . In December 1796 another telegraph line was constructed between the Admiralty and Portsmouth . In May 1806 a telegraph line from Beacon Hill on the Portsmouth line to Plymouth was built . A subsequent telegraph line was built between the Admiralty and Great Yarmouth , thus telegraphs covered the south - east , south - west and East Anglia . Before , messages between Portsmouth and London had taken several hours ( two days for Plymouth ) to reach their destination but now communications between London and Portsmouth took only fifteen minutes . Between London and Hythe it was eleven minutes . Contingency plans . The King made contingency plans in the event of a French landing , with a courtier writing on 13 November 1803 : " The King is really prepared to take the field in case of attack , his beds are ready and he can move at half an hour ' s warning " . Another courtier wrote : The king certainly has his camp equipage and accoutrements quite ready for joining the army if the enemy should land , and is quite keen on the subject and angry if any suggests that the attempt may not be made . . . . God forbid he should have the fate of Harold . The King wrote to his friend Bishop Hurd from Windsor on 30 November 1803 : We are here in daily expectation that Bonaparte will attempt his threatened invasion ; the chances against his success seem so many that it is wonderful he persists in it . I own I place that thorough dependence on Divine Providence that I cannot help thinking the usurper is encouraged to make the trial that the ill - success may put an end to his wicked purposes . Should his troops effect a landing , I shall certainly put myself at the head of my troops and my other armed subjects to repel them . But as it is impossible to foresee the events of such a conflict , should the enemy approach too near to Windsor , I shall think it right the Queen and my daughters should cross the Severn , and send them to your Episcopal Palace at Worcester ; by this hint I do not the least mean they shall be any inconvenience to you , and shall send a proper servant and furniture for their accommodation . Should this event arise , I certainly would rather have what I value most in life remain , during the conflict , in your diocese and under your roof than in any other place in the island . The government ' s contingency plans laid down that the King would go to Chelmsford if the French landed in Essex , or to Dartford if they landed in Kent , along with the Prime Minister and the Home Secretary . Lord Cornwallis would be in command of the reserve army . The Royal Arsenal artillery and stores and the Ordnance Board ' s powder magazines in Purfleet , would be put on the Grand Junction canal to the new ordnance depot at Weedon , Northamptonshire . Soldiers would be paid in gold instead of paper money . The Bank of England books would be sent to the Tower of London and its treasure would be entrusted to Sir Brook Watson , the Commissary General , who would transport it in thirty wagons ( guarded by a relay of twelve Volunteer escorts ) across the Midlands to join the King at Worcester Cathedral . The Stock Exchange would close and the Privy Council would take charge in London . The press would be forbidden from printing troop movements and official government communiqués would be distributed . If London fell to the French , the King and his ministers would retreat to the Midlands and " use the final mainstays of sovereignty – treasure and arms – to keep up the final struggle " . Legacy . By the 1 September 1805 Napoleon ' s invasion camps were empty due to the Grande Armée marching against the Austrians . The Battle of Trafalgar on 21 October relieved British fears of invasion as Admiral Nelson destroyed the combined French - Spanish fleet . However the threat of invasion remained so long as Britain was at war with France . At Tilsit in July 1807 Napoleon and the Russian Tsar Alexander I agreed to combine the navies of Europe against Britain . The British responded with a pre - emptive attack on the Danish fleet at Battle of Copenhagen and they also made sure the French never secured the Portuguese fleet . Captain Edward Pelham Brenton in his " Naval History of Great Britain " noted that after Trafalgar " another French navy , as if by magic sprang forth from the forests to the seashore , manned by a maritime conscription exactly similar in principle to that edict by which the trees were appropriated to the building of ships " . The First Lord of the Admiralty , Lord Melville , noted after the war that given time Napoleon would " have sent forth such powerful fleets that our navy must eventually have been destroyed , since we could never have kept pace with him in building ships nor equipped numbers sufficient to cope with the tremendous power he could have brought against us " .