As the breeze filled the sails of the Frenchmen, Grasse signalled to the convoy to bear away before it to the north-westward, while he with his fighting-ships set his course for the channel between Dominica and Guadeloupe. He rightly judged that Rodney would follow the warships, and thus the convoy would have a good start. The channel towards which the French fleet was heading is known as the Saints' Passage, "not on the surmise that it leads to Heaven,"[14] but because along its northern waters stretches a line of rocky islets known to the French as "les Iles des Saintes." The nine ships of Hood forming the English van had gone far ahead of the rest of the fleet. If De Grasse had not had his mind so centred on the idea of avoiding a battle, there is little doubt that he might have brought an overwhelming force to bear on them. Luckily for Rodney, he contented himself with sending his second in command, Vaudreuil, to skirmish with them, passing and repassing Hood's division at long range and firing at masts and rigging in the hope of disabling them for further pursuit. Hood returned the fire, doing as much damage as he suffered, and towards midday the rest of the English had worked up to him by taking advantage of every breath of wind that blew over the ridges of Dominica. Then the wind fell again, and all through the night and the following day (10 April) the fleets lay in sight of each other beyond even distant cannon shot, Vaudreuil's and Hood's crews busying themselves with repairing rigging and replacing damaged spars.

During the 11th De Grasse tried to get his fleet through the Saints' Passage, working by short tacks to windward, and baffled and delayed by sudden calms. In the afternoon several of his ships were still to the westward of the strait, and Rodney, who had been getting gradually to the northward, despite the frequent failure of the wind under the lee of Dominica, was at last near enough seriously to threaten these laggards. In order to save them from being overwhelmed by the whole English fleet, De Grasse gave up the advantage of weary hours of hard work and came back before the wind out of the strait. At sunset the two fleets lay to the westward of the Saints' Passage, and there was no probability that De Grasse would attempt to tack through it during the hours of darkness. In the night Rodney manœuvred to get to windward of the enemy, and at daylight on the 12th the two fleets were within striking distance, De Grasse to the leeward, his fleet in a straggling line over some nine miles of sea. Rodney had his opportunity of forcing on a decisive battle at last.

At some distance from the French line a partly dismasted line-of-battle ship, the "Zelé," was seen in tow of a frigate. She had been in collision with the flagship during the night, and had been so badly damaged that De Grasse was sending her away to Guadeloupe. Rodney's ships had lost their order of battle somewhat in the darkness, and while he was reforming his line he detached a couple of ships to threaten the disabled "Zelé." This had the effect he intended. It removed De Grasse's last hesitation about fighting. The French line was soon seen bearing down on the port tack, the rearward ships crowding sail to close up. Rodney's battle line, in reversed order, led by Drake and the rear division, was already on a course that would bring the two fleets sweeping past each other, and the leading ship, the "Marlborough," was steered so as to make the passage a close one. Rodney had hoisted the signal to engage the enemy to leeward. While the fleets were closing he sat in an arm-chair on his quarterdeck, for he was older than his sixty-four years, broken by long illness and only sustained by his dogged spirit. One of his captains, Savage of the "Hercules," also went into battle seated in an arm-chair beside the bulwarks of his ship. He was lame with gout and unable to stand or walk without help. When the firing began, and the ships were passing each other amid a thunder of broadsides and a hail of shot and bullets, Captain Savage gravely raised his cocked hat to salute each enemy as she ranged up abreast of the "Hercules." What would those old sailors have thought of the naval commander of to-day peeping through the slits in the steel walls of a conning tower? But it is only fair to ask also what they would have thought of shells weighing half a ton bursting in fiery destruction.

The "Marlborough," approaching on a converging course, came to close quarters with the "Brave," the sixth ship in De Grasse's line, and then, shifting her helm to bring her course parallel to that of the enemy, exchanged broadsides with the Frenchman. Ship after ship came into action in the same way. The speed was nearer three than four knots, and the lines some six miles long, so it was more than an hour before the leading English battleship was abreast of and engaged with the rearmost Frenchman. As ship passed ship there was a thunder of artillery, a rattle of small arms. Then a brief lull till the guns of two more opponents bore on each other. But in this cannonade the English had the advantage of the heavy blows struck by their large-bore carronades at close range, and the fact that their gun-mountings enabled them to keep a passing ship longer under fire than was possible for the French gunners. In De Grasse's ships, crowded with troops, the slaughter was terrible. As the fight went on and the French ships came under the crushing fire of adversary after adversary, it was seen that it was only with difficulty the officers kept the men at the guns. In this first hour of the fight the French began to throw the dead overboard to clear their encumbered decks, and a strange horror was added to the scene, for shoals of sharks that had followed the fleets to pick up anything thrown overboard now swarmed around them, lashing the water into foam as they struggled for their human prey.

At length the leading English ship was abeam of the rearmost of De Grasse's fleet. Over some six miles of sea the two battle lines extended, every ship ablaze with fire-flashes from her guns and with the dense smoke-clouds drifting around the English vessels and wrapping them in the fog of war. If the battle was now to be fought out on the old traditional method, the fleets would clear each other, wear and tack and repass each other in opposite directions with a second exchange of fire. But now came the event that made the battle of the Saints' Passage epoch-making in naval history.

What precisely happened is wrapped in a fog of controversy as dense as the smoke-fog that enveloped Rodney's fleet at the decisive moment. One thing is certain. The old admiral suddenly changed all his plans, and executed a new manœuvre with the signal he himself was disobeying—the order to engage to leeward—still flying from his flagship. The act was the sudden seizing of an unexpected opportunity. But some of the merit of the new departure was due to Rodney's right-hand man, his "Captain of the Fleet," Sir Charles Douglas. Douglas was one of those whose minds had been influenced by new theories on naval war, which were just then in the air. In Britain a Scotch country gentleman, John Clerk, of Eldin, had been arguing for some time in pamphlets and manuscripts circulated among naval officers against the formal methods that led to indecisive results. His paper plans for destroying an enemy were no doubt open to the criticism that they would work out beautifully if the enemy stuck to the old-fashioned ways and attempted no counter-stroke. But the essence of Clerk's theories was that parallel orders of battle meant only indecisive cannonading; that to crush an enemy one must break into his line, bring parts of it under a close fire, not on one side, but on both, and decide the fate of the ships thus cut off by superior numbers and superior gun power before the rest could come to their help. His plans might not work out with the mechanical exactitude described in his writings, but they would tend to produce the close mêlée, where the best men and the steadiest fire would win, and after such an encounter there would not be merely a few masts and spars shot away, and a few holes to be plugged, but the beaten side would be minus a number of ships sunk, burned, or taken, and condemned to hopeless inferiority for the rest of the campaign. Clerk was not the only man who put forward these ideas. A French Jesuit professor of mathematics had worked out plans for securing local advantage of numbers in a sea-fight at close quarters; but while French naval officers laughed at naval battles worked out with a piece of chalk and a blackboard, British sailors were either themselves thinking out similar schemes or were beginning to think there might be something in the Scotch laird's diagrams.

It was at the critical moment when the two fleets lay side by side in parallel lines on opposite courses, wrapped in the battle-smoke, that Douglas, looking out through a gap in the war-cloud, saw that a sudden flaw of wind blowing steadily from the south-east was flattening the French sails against the masts and checking their speed. The same sudden change of wind was filling the English sails, and the masters were squaring the yards to it, while the Frenchmen to keep any way on their ships had to bring their bows partly round towards the English line. Between the "Glorieux," the ship immediately opposed to Rodney's flagship, the "Formidable," and the next Frenchman in the line, the "Diadème," a wide gap was opening up. Douglas saw the chance offered to his admiral. Half the English fleet was ahead of the "Formidable," engaged with the rearward French ships. If the "Formidable" pushed through the gap, leading the rest of the line after her, the French rear would be cut off from the van and brought under a double fire at close quarters, and there would be a fair prospect of destroying it before De Grasse could come back to its support. He rushed to Rodney's side. Moments were precious. He urged his plan in the briefest words. At first the old admiral rejected it. "No," he said, "I will not break my line."[15] Douglas insisted, and the two officers stepped to the opening in the bulwarks at the gangway and looked out. The "Formidable" was opposite the tempting gap in the French line. Rodney in a moment changed his mind, and told Douglas that he accepted his plan.

In the haste to carry it out the signal to fight to leeward of the French was forgotten and left flying. The "Formidable" turned her high bows into the gap, and swept through it with all her hundred guns and her carronades in action, pouring broadside after broadside right and left into the "Glorieux" and the "Diadème." Six ships in succession swung round and followed in the wake of the flagship, which was now engaged with the French on the windward side. Shattered by successive blasts of well-directed fire, the "Diadème" was drifting a helpless wreck, and the rearward ships, with their way checked, were huddling in confusion behind her, English ships firing into them on both sides. Through another gap in the French line, ahead of De Grasse's giant "Ville de Paris," other English ships made their way in the dense cloud of smoke, some of the captains hardly aware of what they were doing. The French van had meanwhile forged ahead, and then, as the wind suddenly fell to a dead calm, it was seen that De Grasse's fleet was broken into three isolated fragments.

To the southward lay the van ships under De Bougainville becalmed, with no enemy in range of them. The "Ville de Paris," with several of her consorts of the French centre, formed another group, with the whole of the rearward English division exchanging fire with them at long range. The rear of the French, under Vaudreuil, and the ships of the centre cut off by Rodney's manœuvre were huddled together, with Hood's division and the ships that had followed the "Formidable" through the line shepherding them. The loss of the wind had made it difficult or impossible to keep the broadsides bearing, and for an hour the action died down into a desultory cannonade. When the breeze came again over the ridges of Dominica, De Bougainville's division, now far to leeward, made no attempt to succour De Grasse. Only one of his ships slowly beat up to the main battle. The French admiral tried to get away to the westward, but Hood clung doggedly to him, while Rodney and Drake completed the defeat of Vaudreuil and the French rear. The "Diadème" soon struck her colours. A frigate tried to tow the dismasted "Glorieux" out of the mêlée, but the captain of the "Glorieux," De Kerlessi, saw that the effort would only end in the friendly frigate being also captured, and with his own hand he cut the tow-rope and hauled down his flag. Then the "César" struck her colours, and while the rearward ships were being thus disposed of, in the broken Centre the "Hector" and the "Ardent" surrendered to Hood's division.

The English attack was now concentrated on the centre, and the battle raged fiercely round the French flagship, distinguished by her huge bulk and her towering masts. One by one these came down, trailing in a tangle of spars, sails, and rigging over her sides. Her crowded decks were a shambles of dead and dying, but still De Grasse fought on—for honour, not for victory. His van held aloof, his broken rear was in flight. Five of his ships had struck. Still he kept his guns in action till Hood in his flagship, the "Princesse," ranged close up alongside of him and poured in a series of destructive broadsides. Then the French flag came down at last, and De Grasse went on board the "Princesse" and gave up his sword to the vice-admiral.