Affairs at Derry were now approaching a crisis. The siege had been pressed with vigor under every disadvantage: minority of force, inadequate artillery, and a season almost unprecedented for heavy rains, which kept the trenches continually filled with water from the beginning to the end of the siege. The besieged, reduced to the last extremity, had become almost passive in their resistance, and were frequently on the point of surrendering, when the appearance of an English fleet would again raise their spirits for a time, but to cause a still greater depression when it had to withdraw without being able to afford relief. Every successive disappointment renewed the murmurs of the people, and cooled the ardor of the soldiers. Several times through the summer they had received fresh supplies of powder and ball; but of provisions, which were as easily smuggled in, they had received little or none.

De Rosen, exasperated by delay, collected the fugitive population of the district, and placing them between the town and his men, gave orders to drive them in on the besieged. The Irish soldiers, though suffering great privations, and eager for the surrender, refused to obey the order, and threatened a mutiny if compelled to enforce it. De Rosen continued unmoved, but Hamilton and the other leaders communicated the circumstance to the king, and received a positive order that the multitude should be allowed to depart unmolested to their homes. The garrison, taking advantage of this circumstance, sent away the most helpless of the citizens, and took in a reinforcement of the young and active in their place, so that de Rosen's cruelty ultimately tended to their advantage.

Yet, notwithstanding the advantage thus gained by the besieged, their suffering had become unendurable, and despair had settled on all, when, towards the middle of July, Kirke again entered Lough Foyle, and displayed his fleet to the wistful eyes of the starving inhabitants, and was again obliged to retire without accomplishing his object. This was the turning-point of the siege. The long-hoped for relief again disappeared; the authorities of Derry determined on a surrender, and demanded a cessation to regulate its provisions. But Kirke managed to convey a note to the governor, concealed in a twisted rope, which he tied round the waist of a country lad, and this note—which may be found in Walker's account of the siege,—apprised him of a plan which he had set on foot to relieve the garrison.

Baffled in his efforts to succor the town from the side of Lough Foyle, Kirke divided his fleet and with one part of it doubled Malin Head, sailed up Lough Swilly, and established a garrison of 800 men near Rathmelton, a few miles west of Derry. The place was well selected for his purpose; which was to attract the attention of the besiegers, and cause them to withdraw some of their forces from the side of the Foyle. This movement was observed by de Rosen, who, instead of drawing his forces from the water-side, ordered Berwick from Enniskillen to check the movements of Kirke, and dislodge him, if possible, without weakening the forces stationed at the obstructions in the river; and Berwick, as already indicated, abandoned Enniskillen, and arrived at Rathmelton, with a force of 1,200 horse, about the 22d of July.

The position occupied by Kirke was one of great natural strength. The inlets of the Lough indented the country in all directions, and extended up to within three or four miles of Derry, presenting almost insuperable difficulties to an attacking force; and, on one of its peninsular mazes, he was found strongly intrenched under the protection of his frigates. Berwick spent a whole day in trying to dislodge him, but without effect, when he retired to an adjacent height, and contented himself with watching his movements, and confining him to his intrenchments.

But Kirke succeeded in his object. Notwithstanding the vigilance of Berwick, he threw both men and munitions into Enniskillen; partially relieved Derry; and conjuring the governor to hold out yet a little longer, sailed out of Lough Swilly, and joined the fleet at the Foyle, while Berwick united his command to the force of the besiegers.

On the 28th of July, the English fleet again appeared in Lough Foyle, and bore up steadily towards the obstructions above Culmore Fort, near the mouth of the river. It consisted of twenty ships of war, 300 transports laden with provisions and military stores, and 6,000 veteran troops under the command of General Kirke.[20] The result may be anticipated. The blockading army, not having cannon of sufficient calibre to sink the approaching vessels, the boom across the river was broken. Derry was partially relieved on that day, and, on the 30th, all attempts of the besiegers to thwart their movements had become futile. The whole fleet rode up the river, and succored the beleaguered town, and the Irish army, after a few days more, raised the siege, and retired towards Dublin, on which Marshal Schomberg was reported to be projecting a descent. On their way they were joined by the remnant of Mountcashel's command; nor was the news that preceded them in Dublin of a more cheering character. Since the siege had commenced, the famous battle of Killicrankie had been fought and won. There, on the 26th of May, Dundee, at the head of 2,000 Irish, and about the same number of Highlanders, defeated General Mackay's army of 8,000 veterans. But with this victory expired the hopes of the Jacobite cause in Scotland. Dundee received a mortal wound in the moment of victory; the Highlanders, dispirited by his death, dispersed after a few unimportant skirmishes, and what was left of the Irish contingent returned to their own country.

So ended the siege of Derry, an affair of little military note, but of great political and religious import. Though its gates were closed against the king's troops on the 7th of December, free access to it from the sea was not obstructed until the surrender of Culmore, on the 21st of April. It had made ample preparation for a siege, and, notwithstanding the blockade, had received 480 barrels of gunpowder, and stores of provisions and clothing, from that time until the end of June. It had not been closely invested until the latter part of May; and, unless from the two light field-pieces of General Wauchop, on the water-side, there was no cannonade whatever before the 21st of June, when Berwick withdrew to Enniskillen. The defenders, during the heat of the siege, had other advantages not generally accorded to an enemy. They were allowed to send away ten thousand of the sick and indigent inhabitants, and, during the armistice that ensued, had managed to admit an equal number "of the young and active." They had thirty siege-guns on their walls, 10,000 "regimented men," and a population, stated at twenty thousand, to supply the casualties of war.

The investing force was 5,000 men, four siege-guns, two mortars, and two field-pieces. From this force 400 dragoons marched with the Duke of Berwick to Enniskillen, and during the siege they received but 2,500 additional troops, making the entire force 7,500 men. The weather was continually unfavorable to siege operations, and, excepting in the amount of rations, the besiegers endured far more suffering than the besieged. The bombardment continued at intervals from the 21st of June to the 28th of July; but during the last week there had been an almost entire cessation of hostilities, to admit of negotiations. On the estimate of the Reverend George Walker, who has left a journal of the siege, the ball and mortar, great and small, thrown into the town up to the 22d of July, was 587. After this there was but an occasional shot until the siege was raised. This fell short of fifteen shots a day, and about one every two hours, admitting them to have been fired in regular succession. During the siege the garrison had been reduced to 3,000 effective men, while the besiegers retired with 3,500—showing a loss to the defenders of 7,000, and to the assailants of 3,600.

The Duke of Berwick, who was present in all the skirmishing that took place up to the 21st of June, and who afterwards became a prominent character in the great wars of the continent, had certainly no inducement to magnify this episode in his life, by underrating the Jacobite forces; nor is it to be credited that the Reverend George Walker has given an overestimate of the besieged. Whatever were the privations of the non-combatants,—and they must have been great—it does not appear from his journal that the defenders were, for any considerable time, on an allowance much below that of soldiers in ordinary warfare. We find that in two or three instances they were obliged to resort to the boiling of salt hides for a substitute; and to eating "dogs and cats, etc.," now considered a luxury, though thrown in by Williamite writers to shadow a picture dark enough from any perspective.