It was then resolved to besiege Ariancopang in form; but here as at Carthagena the engineers proved to be utterly ignorant of their business, and blunder succeeded blunder. Paradis, who had a troop of sixty horse in addition to the infantry of his garrison, judged astutely of the moral effect which cavalry might produce on seafaring men, and sent his handful of troopers, with infantry in support, straight at the trenches of the naval brigade. The sailors were seized with panic; the panic spread to the regular troops, and the whole rushed headlong back to the camp, leaving their best officer, Stringer Lawrence, to be taken prisoner. Accident, however, came to the help of the British. A magazine at Ariancopang caught fire and exploded, disabling over one hundred men; and the garrison having dismantled the fortifications withdrew into Pondicherry. Boscawen accordingly moved forward from Ariancopang and opened his trenches against the north-western corner of the town. Then once more the ignorance of the engineers led to blunders and waste of time, for they opened their first parallel at a distance of fifteen hundred yards, or twice the distance prescribed by rule and common sense, from the covered way. Still fortune for the present favoured the British. A sortie made by the French was brilliantly repulsed, and Paradis, the ablest of the French both as officer and engineer, was wounded to the death. The Englishman most distinguished in this affair was to prove himself Paradis's most brilliant pupil, an ensign in the Company's service, taken only twelve months before as a clerk from the Company's desks, Robert Clive.

The success of the British now appeared so certain that the Nabob Anwarudeen, yielding to the repeated gifts and appeals of Boscawen, decided to throw in his lot with them and promised to furnish a body of two thousand horse. Still Dupleix was not discouraged. By the death of Paradis the chief burden of military as well as of civil command was thrown upon his shoulders, but he did not shrink from it. After all, if he were no soldier, neither was Boscawen. By immense labour the British trenches were carried forward to the position from which they should have been opened, eight hundred yards from the wall, and early in October two batteries at last opened on the town. They were answered by twice as formidable a fire from the guns of the besieged. Boscawen then ordered the fleet to open fire from the sea, but the ships being prevented by shoal water from approaching nearer than a thousand yards from the works, the cannonade was wholly ineffective. The fire of the British batteries ashore continued for three days with little result, while that of the besieged increased rather than languished. The rainy season then set in earlier than usual; the trenches were flooded, and disease began to rage in the British camp. Finally, on the 11th of October, Boscawen decided to raise the siege and the British retreated, leaving over one thousand Europeans dead behind them, while Dupleix remained proud and unconquered in Pondicherry.

The failure of this enterprise was due to the same causes that had wrecked the expedition to Carthagena. In the first place, Boscawen arrived on the coast too late. In the second, he wasted nearly three weeks over the capture of Ariancopang, which was not essential to the capture of Pondicherry. In the third, the unskilfulness of the engineers prolonged the operations, and occupied the troops with duties which kept them from active service in the trenches and harassed them to death for no purpose. The experiment of setting a naval officer in charge of highly technical military operations was probably due to the influence of Vernon; to which also may be traced Boscawen's readiness to attempt the storm of Ariancopang after Vernon's rough-and-ready manner. Against Spaniards in South America such methods might have succeeded; against Frenchmen they could not, least of all when commanded by a Dupleix with a Paradis for his military adviser. If the failure before Pondicherry had ended with the raising of the siege, the reverse would have been comparatively a trifling matter; but it told far and wide over India as a blow to British influence and prestige, and Dupleix was not the man to neglect to magnify the success and the greatness of his nation.

The news of the peace of Aix-la-Chapelle some months later brought about a cessation of overt hostilities and the re-delivery of Madras to Boscawen; but still the war did not end. As in Europe French and English could fight fiercely as auxiliaries of an Elector of Bavaria and a Queen of Hungary, so in Asia they could carry on, as allies of native princes, the contest which was to determine the fate of India.