The arrival of three Spanish frigates with arms and ammunition in Donegal Bay was welcome news to the Northern Catholics. They were delivered to O'Donnell, who was incessantly in the field, while O'Neil was again undergoing the forms of diplomacy with a new royal commission at Dundalk. He himself disclaimed any correspondence with the King of Spain, but did not deny that such negotiations might be maintained by others. It is alleged that, while many of the chiefs had signed a formal invitation to the Spanish King to assume their crown, O'Neil had not gone beyond verbal assurances of co-operation with them. However this may be, he resolved that the entire season should not be wasted in words, so he attacked the strong garrison left in Armagh, and recovered the primatial city. According to the Irish practice, he dismantled the fortress, which, however, was again reconstructed by the English before the end of the war. Some other skirmishes, of which we have no very clear account, and which we may set down as of no decisive character, terminated the campaign.
In May, 1597, Lord Borough, who had distinguished himself in the Netherlands, replaced Russell as Lord Deputy, and assumed the command-in-chief, in place of Sir John Norris. Simultaneously with his arrival Feagh Mac Hugh O'Byrne, was surprised in Glenmalure by a detachment from Dublin, and slain; he died as he had lived, a hero and a free man. O'Neil, who was warmly attached to the Wicklow chief, immediately despatched such succour as he could spare to Feagh's sons, and promised to continue to them the friendship he had always entertained for their father. Against Tyrone the new Lord Deputy now endeavoured to combine all the military resources at his disposal. Towards the end of July, Sir Conyers Clifford was ordered to muster the available force of Connaught at Boyle, and to march into Sligo and Donegal. A thousand men of the Anglo-Irish were assembled at Mullingar, under the command of young Barnewell of Trimbleston, who was instructed to effect a junction with the main force upon the borders of Ulster. The Lord Deputy, marching in force from Drogheda, penetrated, unopposed, the valley of the Blackwater, and entered Armagh. From Armagh he moved to the relief of the Blackwater fort, besieged by O'Neil. At a place called Drumfliuch, where Battleford Bridge now stands, Tyrone contrived to draw his enemies into an engagement on very disadvantageous ground. The result was a severe defeat to the new Deputy, who, a few days afterwards, died of his wounds at Newry, as his second in command, the Earl of Kildare, did at Drogheda. Sir Francis Vaughan, Sir Thomas Waller, and other distinguished officers, fell in the same action, but the fort, the main prize of the combatants, remained in English hands till the following year. O'Donnell, with equal success, held Ballyshannon, compelled Sir Conyers Clifford to raise the siege with the loss of the Earl of Thomond, and a large part of his following. Simultaneously, Captain Richard Tyrrell of West-Meath—one of O'Neil's favourite officers—having laid an ambuscade for young Barnewell at the pass in West-Meath which now bears his name, the Meathian regiment were sabred to a man. Mullingar and Maryborough were taken and sacked, and in the North, Sir John Chichester, Governor of Carrickfergus, was cut off with his troop by MacDonald of the Glens.