In retrospect, we know that Napoleon had already just about given up on his ambition to invade Britain, but nobody in Britain could have been anywhere close to knowing that in October 1805 and anyway, had the unthinkable happened and the Franco-Spanish fleet inflicted any sort of defeat on Nelson, it is more than possible that Napoleon would have had a quick change of thinking.

So, as Nelson prepared for the confrontation, there was only one thing on his mind - deliver a huge body blow to the enemy and crush any French ambitions of attaining mastery of the waves - no matter how temporary.

And Nelson had been planning for this moment for a long time, with a battle plan based on every action he had taken part in during his long and illustrious career.

In his opinion - and it’s a historical fact - too many naval engagements ended with one side scraping a tactical win and without the “victor” hammering home the advantage; often, the “losing” fleet would withdraw, fairly intact, to find its nearest home port in which to repair the damage sustained and then to come out again, maybe months later, still able to mount a threat.

What Nelson wanted above all - and also believed was possible - was to inflict a defeat of such proportions that the French fleet would require several years, ever to be able to risk leaving port again, let alone offering serious opposition.

To that end, he had devised his “master plan”, which would enable him to use his superior gunnery, superior seamanship and better training - and it was all, especially with the benefit of that most precise of sciences, hindsight, so very simple ...

The traditonal naval battle tactic was for two fleets to sail parallel to each other and pound away with broadside fire; the side which could fire faster and with more accuracy would inflict the greater damage and the losing side would withdraw.

Over the years - and Francis Drake had been the first to try the tactic - various commanders had exploited the tactic of cutting the enemy line in two and of getting some ships behind the enemy line, in an effort to gain the advantage of numbers in the crucial area of the engagement.

Now, Nelson had an even better idea - he would cut the Franco-Spanish line in two places, using the advantage of the wind, isolate half the opposing fleet and, before the remainder of it could tack against adverse conditions, blitz that half of the enemy’s vessels that had thereby been isolated from the rest.

Furthermore, this was not some recently and hastily conceived plan - Nelson had been carefully working on it for a long time and had drafted written instructions, which he had gone over with his various commanders at great length.

So, as his fleet sailed towards Villeneuve’s somewhat dispirited force, every man in his command knew exactly what was expected of him and - perhaps more importantly - exactly what he could expect from every man around him ...

In contrast, Villeneuve’s main battle plan seems to have been, once again, to try to run Nelson out into the open sea, to keep some sort of distance between the two fleets and maybe just to engage in peripheral confrontations.

In order to achieve that, he had initially ordered a squadron under the command of Rear Admiral Charles René Magon de Médine to sail from Cadiz ahead of the main fleet and either capture, or drive off the British frigates which were patrolling the waters, waiting to feed information back to Nelson.

Unfortunately for him, as Magon weighed anchor, the wind dropped considerably and only seven battleships and three frigates made it out of Cadiz - the lack of breeze then made it impossible for Magon;s force to chase the British frigates and the news was sent back to Nelson that the French were, at last, on the move.

With the threat of the “axe” at his back, Villeneuve was forced to bring the rest of his fleet out of harbour and try to make some sort of stand. Perhaps he hoped for a miracle and that his numerical supremecy would make the difference when it came to it.

Whatever his thinking, early on 21 October, the two fleets were in sight of each other and a full-scale battle was inevitable ...

Shortly after dawn on 21 October, the French frigate Hermione spotted the British fleet, to windward, in the west and signalled this information to Villeneuve, aboard the Bucentaure - the French commander wavered for several minutes, trying to decide upon the best course of action.

He had, in fact, worked out roughly what form Nelson’s attack would take, but he had failed to issue his captains with any proper defensive plans. Now, positioned off a lee shore, he decided this was not the proper place to engage the British and, where he could have continued sailing on towards Gibraltar, instead he gave orders for the fleet to turn and head back towards Cadiz.

The order to “wear” took a few hours to execute and wasn’t completed until about 10 am and now the inferior seamanship of some of the crews of the Combined Fleet was exposed, as many vessels were finding it almost impossible to regain their position in the battle line, thanks to the light wind.

Admiral Gravina’s observation squadron, which consisted of his flagship Principe de Asturias and several frigates, should have taken station to the west of the main fleet, from where the wind would have enabled it to sail quickly to assist any part of Villeneuve’s line that was threatened by the British, but had ended up nearthe van.

Now, in the confusion of turning the fleet, Gravina’s squadron had ended up nearer the rear and to the lee of the main line, meaning that it would have to sail into the wind, in order to reinforce against any British break-through manoevre.

Aboard HMS Royal Sovereign Collingwood could see this weakness and the information was signalled to Nelson, who was further to the north. The situation was all and more that Nelson could have hoped for.

Villeneuve frantically signalled Gravina to change course and move to his windward, as it became clear that the British were now approaching in two columns and would cut through the Franco-Spanish line in such a way that the van of the Combined Fleet would be cut off from the main battle for some hours.

On board HMS Victory, Nelson summoned Lieutenant Pasco and ordered him to make a signal to the fleet.

‘Mr Pasco,’ he said, ‘I wish to say to the fleet: “England confides that every man will do his duty”.’

Pasco requested that he be permitted to substitute the word “expects” for “confides”, as “expects” was in the telegraphic vocabulary and had its own flag, whereas “confides” would need to be spelled out and Nelson agreed.

The changed word altered the meaning of the signal subtly and caused some confusion among the sailors in the British ships, with many muttering that they would always do their duty and didn’t have to be asked.

Minutes later, a final signal was run up the Victory’s mast - “Engage the enemy more closely” - and the two British lines closed upon the enemy.

Soon after this, the first shots were fired by the Combined Fleet at Royal Sovereign, as she came within range. Collingwood held his nerve and his fire for several more minutes and then, at noon, gave his order to open fire.

Minutes later, the first enemy ships opened fire on Victory, as she bore down upon the line at the point where Villeneuve’s Bucentaure sailed just astern of the Spanish ship Santissima Trinidad.

In typical Nelson style, he had decided to go straight for the throat and engage his opposite number, by smashing through the line astern of Bucentaure and raking her stern with carronade fire.

This, in itself, was not a new tactic - the weak point of wooden battleships was their stern, for heavy shot crashing through the stern walls could fly straight down the length of the gun decks, sweeping everything before it and the carronade had been designed for just this purpose.

Firing 64 pounds of shot or musket balls, unlike the standard 32-pounder broadside guns, the carronade was not designed for long range bombardment, but at close range it was deadly - which is why carronades were nicknamed “smashers”.

On the fo’castle of Victory, the Bosun, William Willmet, waited with the port carronade primed and loaded with a huge roundshot and a keg of five hundred musket balls ...

Further aft, there was great concern among his officers for Nelson’s safety, as he had insisted on wearing all his insignia and decorations, which made him an obvious target, but Nelson seemed disinterested in their worry.

Indeed, it seemed to them that he had already made up his mind that he was going to die and spent some time going round old friends aboard and bidding them farewell, also giving instructions to ensure that Lady Hamilton and his daughter would be well cared for.

Captain Blackwood suggested that Nelson might move his flag to HMS Euryalus and direct the battle from there, but Nelson would have none of it, although he was concerned for the safety of the men under him.

As Victory came under increasing fire, men began to fall, including Nelson’s secretary, John Scott and one shot killed eight marines stationed on the poop deck.

Seeing this, Nelson ordered the Captain of Marines, Charles Adair, to disperse his men about the ship and this order may well have cost Nelson his life ultimately, for the marines would have been able to deal with any French sharpshooters stationed in the rigging.

Meanwhile, the range was closing with every second and, still under terrible French fire, Victory finally broke through astern of Bucentaure, the two ships almost within touching distance.

Willmet discharged the carronade, with deadly effect and, as Victory passed behind the French flagship, one by one her port 32-pounders fired into the stern of Villeneuve’s massive vessel.

As Victory cleared Bucentaure, she came with in range of the French battleship Neptune, which fired a broadside into her, damaging the foremast and bowsprit.

Captain Hardy ordered the helm hard over and brought Victory alongside the smaller Redoutable and, as she drew level, the starboard batteries began discharging a deadly hail of cannon fire into the French ship.

The two vessels crashed against one another and their rigging locked; the French sailors closed most of their port gunports, in order to prevent boarding and French marines in the rigging threw down grenades and musket fire.

Then, at about 1.15 pm, as Nelson and Hardy walked on the quarter deck, a musket ball struck Nelson on the top of his shoulder and smashed downwards, into his spine.

He realised immediately that the wound was fatal and cried out to Hardy that the French had done for him at last, as his backbone was shot through and, as he was carried below, he insisted that his face be covered with a handkerchief.

Meanwhile, HMS Téméraire, which had been the second British ship through the French line, closed on the opposite side of Redoutable and the three ships became locked together; the two British ships steadily pounded the sandwiched French ship into submission.

To the south, Collingwood had engaged the rear of the Combined Fleet line, but, unlike Nelson, at the last moment he ordered his ships to turn broadside on and set up a tremendous barrage of fire.

At this point, the enemy line was closed up in a loose formation, rather than an orderly line and Collingwood’s ships were faced with a confused array of vessels and a mixture of French and Spanish commanders, which made organised opposition impossible.

Initially, Collingwood’s Royal Sovereign had engaged the Santa Ana and Fougueux alone, having gained some distance on the remainder of the British line and, for about thirty minutes, the British gunners fought against opposition from two sides - fortunately, the enemy gunners were not in the same league and Royal Sovereign gave more than she got.

By now, the already light wind was dying away and, with masts and rigging severely damaged, or, in some cases, shot away completely, ships of both sides drifted about, trying to find targets in the confusion.

It is hard for us to imagine the scene, but the repeated discharge of so many cannon had created a massive pall of smoke, reducing visibility to a few yards in places, so that the remainder of the battle was slogged out in the middle of what must have been as bad as any Victorian London pea-souper fog.

Two hours after battle was first joined, the Combined Fleet, now under Admiral Dumanoir, finally began to wear or tack and sail away from the scene; four ships, including Dumanoir’s Formidable sailed to the windward of the British and exchanged shots as they passed, but that was all.

Only the Intrepide and Neptuno tried to come to Villeneuve’s aid and the former, engaged by several British ships, was singled out for gallantry by several British captains, in the aftermath of the battle.

Slowly but surely, the British ships gained the upper hand over the remaining enemy ships, as one by one they either struck their colours, or turned about and sailed away from the terrible scene.

Seeing that victory was now assured, Captain Hardy went below, to the cockpit, where the surgeon, William Beatty, had done his best - but to no avail - and gave the news to the dying Nelson.

The world’s greatest naval commander sighed and closed his eyes.

‘Thank God I have done my duty, Hardy,’ he said.

Shortly after, he died and a nation would celebrate and mourn at the same time, happy that the threat of French invasion was sunk for all time, but shedding tears of grief for the passing of their hero, who had been snatched from them at the moment of his greatest triumph ...

Nelson’s death certainly took the gloss off the British victory and it is impossible for us now to comprehend the effect that news of his passing would have had on his officers and crews and upon the people waiting anxiously back in Britain.

Horatio Nelson wasn’t just a hero, he was the hero - the outpouring of national grief and the scale of his state funeral were unequalled in memory at the time - and to lose him at the height of his success was a bitter blow to the nation.

Bitter, but probably not as bitter as Nelson would have been, had he known the treatment a supposedly grateful nation was to hand out to his beloved Emma and Horatia.

The government made his brother William an earl, with an annual pension of £99,000 - where was he, when the cannon were roaring and the musketry crackling amidst the smoke and blood of Trafalgar - and Fanny Nisbet, still officially Nelson’s wife, was granted £2,000 per year.

Emma and Horatia received nothing and, without the pension from a grateful nation that Nelson had anticipated for her - and always famous for her extravagant tastes - Emma sank slowly into poverty and even spent time in prison for debt.

When she was finally released, she took Horatia and went to live in Calais, where she died in January 1815, ironically just months before Napoleon Bonaparte met his ultimate Waterloo at the hands of the Duke of Wellington.

So much for a grateful nation ...