The month of August was a month of general rejoicing for the Williamites of Ulster, De Rosen and Berwick had retreated from Derry; Sarsfield, on his way to join Mountcashel, fell back to Sligo on hearing of his defeat at Newtown-Butler; Culmore, Coleraine, and Ballyshannon, were retaken and well supplied; fugitives returned triumphantly to their homes, in Cavan, Fermanagh, Tyrone, and Armagh. A panic created by false reports spread among his troops at Sligo, compelled Sarsfield to fall still further back to Athlone. Six months after his arrival, with the exception of the forts of Charlemont and Carrickfergus, King James no longer possessed a garrison in that province, which had been bestowed by his grandfather upon the ancestors of those who now unanimously rejected and resisted him.
The fall of the gallant Dundee in the battle of Killicrankie, five days before the relief of Derry, freed King William from immediate anxiety on the side of Scotland, and enabled him to concentrate his whole disposable force on Ireland. On the 13th of August, an army of eighteen regiments of foot, and four or five of horse, under the Marshal Duke de Schomberg, with Count Solmes as second in command, sailed into Belfast Lough, and took possession of the town. On the 20th, the Marshal opened a fierce cannonade on Carrickfergus, defended by Colonels McCarthy More and Cormac O'Neil, while the fleet bombarded it from sea. After eight days' incessant cannonade, the garrison surrendered on honourable terms, and Schomberg faced southward towards Dublin. Brave, and long experienced, the aged Duke moved according to the cautious maxims of the military school in which he had been educated. Had he advanced rapidly on the capital, James must have fallen back, as De Rosen advised, on the line of the Shannon; but O'Regan, at Charlemont, and Berwick, at Newry, seemed to him obstacles so serious, that nearly a month was wasted in advancing from Belfast to Dundalk, where he entrenched himself in September, and went into winter quarters. Here a terrible dysentery broke out among his troops, said to have been introduced by some soldiers from Derry, and so destructive were its ravages, that there were hardly left healthy men enough to bury the dead. Several of the French Catholics under his command, also, deserted to James, who, from his head-quarters at Drogheda, offered every inducement to the deserters. Others discovered in the attempt were tried and hanged, and others, still suspected of similar designs, were marched down to Carlingford, and shipped for England. In November, James returned from Drogheda to Dublin, much elated that Duke Schomberg, whose fatal camp at Dundalk he had in vain attempted to raise, had shrunk from meeting him in the field.