William's military commander in Scotland was General Hugh Mackay, head of the veteran Dutch Scots Brigade.
His force of 3,500 included the Brigade regiments of Mackay, Balfour and Ramsay, the English Hastings Regiment and two newly raised Scots units.
When Ewen Cameron of Lochiel learned of William's landing, he began recruiting men to fight for James but the short-term nature of clan warfare meant it needed to be used as soon as possible.

In April, Dundee joined him at Glenroy and on 18 May, took his force of around 1,800 Highlanders and attempted to bring Mackay to battle.
He failed to do so and returned in June, after which most of the clansmen went home, leaving him with less than 200 men.
On 27 June, Dundee wrote to the Earl of Melfort asking for reinforcements; the loss of Kintyre after the Battle of Loup Hill made resupply from Ireland extremely difficult and the letter details alternative landing spots.
As time went on, his position weakened due to continued defections, the surrender of Edinburgh Castle on 14 June being especially discouraging.

His requests for additional resources were denied, partly due to an internal dispute with the Catholic 'Non-Compounders,' who dominated James' court in Ireland and urged him to refuse any concessions to regain his throne.
Dundee and other Scottish Jacobites were mostly Protestant 'Compounders', for whom concessions were essential, and thus viewed with suspicion.
The only reinforcements sent to Scotland were 300 Irish soldiers under the Catholic Alexander Cannon, who landed near Duart Castle on 21 July.
 
A 'Jacobite' garrison under Patrick Stewart of Ballechin occupied Blair Castle, a strategic point controlling access to the Lowlands and seat of the Duke of Atholl.
This illustrates how many families balanced both sides; claiming ill-health, Atholl went to England, leaving his eldest son, John Murray, to 'besiege' his ancestral home.
Stewart himself was a trusted family retainer and one of Atholl's key lieutenants in the suppression of Argyll's Rising in 1685.

In late July, Jacobite reinforcements arrived at Blair; Murray withdrew and Mackay moved north to support him, with somewhere between 3,600 to 5,100 troops.
Seeing a chance to intercept, Dundee set out with his available forces, ordering the clans to follow "with all haste."
Lochiel's sons were sent to raise additional levies; he and 240 Camerons plus Cannon's Irish contingent reached Blair on 26 July.
William's military commander in Scotland was General Hugh Mackay, head of the veteran Dutch Scots Brigade. His force of 3,500 included the Brigade regiments of Mackay, Balfour and Ramsay, the English Hastings Regiment and two newly raised Scots units. When Ewen Cameron of Lochiel learned of William's landing, he began recruiting men to fight for James but the short-term nature of clan warfare meant it needed to be used as soon as possible.
In April, Dundee joined him at Glenroy and on 18 May, took his force of around 1,800 Highlanders and attempted to bring Mackay to battle. He failed to do so and returned in June, after which most of the clansmen went home, leaving him with less than 200 men. On 27 June, Dundee wrote to the Earl of Melfort asking for reinforcements; the loss of Kintyre after the Battle of Loup Hill made resupply from Ireland extremely difficult and the letter details alternative landing spots. As time went on, his position weakened due to continued defections, the surrender of Edinburgh Castle on 14 June being especially discouraging. 
His requests for additional resources were denied, partly due to an internal dispute with the Catholic 'Non-Compounders,' who dominated James' court in Ireland and urged him to refuse any concessions to regain his throne. Dundee and other Scottish Jacobites were mostly Protestant 'Compounders', for whom concessions were essential, and thus viewed with suspicion. The only reinforcements sent to Scotland were 300 Irish soldiers under the Catholic Alexander Cannon, who landed near Duart Castle on 21 July.  
A 'Jacobite' garrison under Patrick Stewart of Ballechin occupied Blair Castle, a strategic point controlling access to the Lowlands and seat of the Duke of Atholl. This illustrates how many families balanced both sides; claiming ill-health, Atholl went to England, leaving his eldest son, John Murray, to 'besiege' his ancestral home. Stewart himself was a trusted family retainer and one of Atholl's key lieutenants in the suppression of Argyll's Rising in 1685.
In late July, Jacobite reinforcements arrived at Blair; Murray withdrew and Mackay moved north to support him, with somewhere between 3,600 to 5,100 troops. Seeing a chance to intercept, Dundee set out with his available forces, ordering the clans to follow "with all haste." Lochiel's sons were sent to raise additional levies; he and 240 Camerons plus Cannon's Irish contingent reached Blair on 26 July.
Battle of Killiecrankie