The Brest fleet finally sailed on 6 September. But lack of wind, the mutinous disposition of the crews and the poor state of repair of the ships caused further delays. Bompard was forced to put in at Camaret, just out from Brest, only finally emerging on 16 September. London had been receiving precise details of the Brest preparations from the outset. Humbert had already surrendered, the Dutch vessels were blocked in port, and Tandy's tiny force was on the point of sailing away from Ireland, having learnt of the collapse of resistance there. So much time had elapsed since Humbert's departure, over a month before, that Hardy's and Bompard's venture was suicidal. Fully alerted and prepared, the British fleet simply chose its moment. The French were spotted by two English frigates, which alerted the main blockading fleet and tracked Bompard's flotilla until it arrived off the Irish coast, despite a massive and time-consuming detour by the French out into the Atlantic. Lough Swilly, their destination, had been the object of intensive naval screening since a defence report of April had confirmed Turner's intelligence that it was the most likely place for a French landing.

A severe storm broke just as the French neared the northern Irish coast. Too heavily laden for easy manoeuvrability and already damaged by the voyage, they were chased by Sir John Borlase Warren and forced to join battle at dawn on 12 October. The Hoche put up a stubborn defence and the battle raged until the afternoon. Casualties on board were high; some 200 men were killed or wounded, and by mid-morning medical stations were reporting their inability to cope. Tone commanded one of the batteries and would have been in the thick of the battle. In howling seas, its main topmast gone, its sails in tatters, the Hoche struck and was sinking with five feet of water in its hold, when it was finally surrounded and captured. Most of the accompanying frigates were chased and taken in separate engagements. Only three of the ten ships which had sailed with Bompard a month earlier made it back to France.