On July 22, 1805, the Britsih fleet under Vice-Admiral Calder, confronted a comined Franco-Spanish fleet, led by Admiral Villeneuve.
Vice-Admiral Calder's fleet :
15 Ships of the Line
2 Frigates
2 Smaller vessels
Admiral Villeneuve's fleet
14 French ships of the Line
6 Spanish ships of the Line
7 Frigates
2 Brigs
During the first engagement, on July 22, the British warship Malta found itself surrounded by five Spanish ships and was sunk. The rest of the battle was undecisive, with the two fleets drifting apart from 27 km on July 23. However, on July 24, a change in the wind gave the Franco-Spanish the ideal position for attack. In the next engagement, the Franco-Spanish fleet sunk the 2 British frigates and 3 Ships of the Line while losing one Frigate. The French also managed to capture Vice-Admiral Calder's flagship, Prince of Wales, as well as the 2 Small british vessels and another Ship of the Line.
The remaining British fleet then retreated to the Home Islands while Admiral Villeneuve pushed northwards. [1]
When the news of Calder's defeat reached Britain, Panick occured in the British government. The British then decided to recall every ship they could to defend the Channel. Meanwhile, Admiral Villeneuve entered Brest with his squadron where he joined force with Admiral Ganteaume. Learning of this, Napoleon was very pleased and gave Villeneuve the Legion d'Honneur while also appointing him as head of the French fleet.
After some days of reparation, the French Armada left Brest for Boulogne, making several stops on the way. Some skirmishes happened between the French and British fleets, but never on a large scale. This skirmishes however, combined with rough weather, would give Britain a recess : the fleet only reached Boulogne on August 26. The next day, Napoleon postponed the invasion and decided to move east to get rid of the Austro-Russian threat. [2]
This culminated with the spectacular Ulm Campaign that ended on December 2, 1805 at Austerlitz where the French forces under Napoleon I defeated those under Czar Alexander I of Russia and Emperor Francis I of Austria and which put an end to the Third Coalition. While the Emperor was doing this, the French fleet was anchoring in the North of France, undergoing repairs and amassing some more ships including the former HMS Prince of Wales which became the French vessel l'Empereur and became the Flaghsip of Admiral Villeneuve.
The invasion was finally launched on March 16, 1806 : the French fleet, numbering around 60 ships of the line, left the port to escort around 250,000 french soldiers and 70 canons in a flotilla of invasion barges. The British had used their time to prepare their defenses and had managed to amass roughly 50 ships of the line in the Channel, under the command of Horatio Nelson and his flagship, the Victory [3].
At 11:00, the Battle of the Channel, the greatest naval battle Europe had ever seen, began. The main event of the battle was the duel that opposed the French flagship l'Empereur to its British counterpart Victory. Admiral Villeneuve was once again [4] defeated by Admiral Nelson but neither Admiral would survive to speak of this : the French Admiral sunk with his flagship and drowned while Nelson was hit by a canon ball and killed.
But even without the two Admirals, the British and French fleet would face each other for 12 hours. At the end of the battle, no clear victor could be decided between the two fleets: the British had lost 10 ships of the line while the French lost 16. Yet, the battle was a tactical defeat for the British : Napoleon, at the head of the flotilla, snuk out of the Battle and managed to land in England, in Kent.
On March 17, at the Battle of Dover, Napoleon inflicted a crushing defeat to the British. He then moved fast towards London which he reached by April 1st. On his way, he had defeated the British army at Canterbury on March 20, Chatham on March 26 and finally the last line of the Capital's defense at the battle of the Thames on March 31. Until Napoleon hismelf entered the city, the Londonians believed it to be a bad joke. They were not the only ones : King George III had refused to leave as, in his madness, he hadn't believed Napoleon was here. He was duly seized by the French, along with most of his family and some members of the government. George, The Prince of Wales, evaded capture as he had already fled the capital on March 29 and was in Northampton. There, he assembled the most of the British army, preparing for a counter-attack as, to him, London's fall was inevitable.
But once again, Napoleon privailed. At the Battle of Bedford, on April 6, the British were definitely crushed and defeated. The Prince of Wales had no other choices but to ask Napoleon for peace. In the subsequent treaty, the treaty of Cambridge, Napoleon imposed the following terms :
-Ireland was to be given independance.
-The British would return French colonies in the West Indies.
-Britain would have to pay 1 Million Francs for the invasion.
-The British wouldn't wage war on France or her allies for the next ten years.
-The British fleet would not attack French ships and would surrender every first rate ship over 80 guns to France.
This was what Georges of Wales managed to negociate. In his original plan, Napoleon had planned to give Scotland Independance, to transfer control of India to France and the surrender of every British first rate ship to the French Navy. It is also said that he had wished for every Dutch east indies to be returned to France, but as Napoleon had few interests there, there is no proof.
Britain's defeat would end the British's participation in the Napoleonic Wars. On the continent, Napoleon definitely reigned supreme after Prussia and Russia were crushed in the War of the Fourth Coalition three month later. In 1807, l'Empereur had become the Master of Europe.
[1] This is my POD. The Battle of Cape Finisterre went much differently OTL. The Malta was indeed surrounded by five spanish ships but he wasn't sunk and managed to capture two spanish ships. There was indeed a favorable wind for the French on July 24, but Villeneuve never ordered the attack and retreated south. Thus, while in OTL the British had a tactical victory, here it ends in a total disaster for the British.
[2] In OTL, Napoleon left Boulogne on August 27 to deal with the Austrians because Villeneuve didn't show up. Here, while Villeneuve does show up, Napoleon choose to first deal with the Austro-Russians.
[3] Since there was no Trafalgar, Neslon is still alive at that time.
[4] There was no Trafalgar, but Villeneuve was at the Battle of the Nile when Nelson destroyed the French fleet of the Egyptian Campaign.