The decision to attack Argyll was driven by both strategy and clan politics -- Argyll's forces threatened the lands of several of Montrose's key supporters. The flank march that followed became one of the legendary feats of the Scottish wars. Montrose's men moved south through the Great Glen and then struck west through terrain that was difficult in summer and potentially lethal in winter. They crossed snowbound passes, forded icy rivers, and navigated ground so rough that the watercourses leading from Glen Buck to Carn na Larach -- terrain the army traversed -- remain challenging for fit hillwalkers even today. The Confederate Irish troops, two thousand experienced soldiers sent from Ireland under Alasdair Mac Colla at the instigation of the Earl of Antrim, had been hardened by years of warfare. The Highlanders, many of them from Clan Donald, were motivated by generations of enmity with the Campbells. Together, they arrived at Inverlochy on the morning of 2 February 1645 -- exhausted, half-starved, and ready to fight.

Argyll's force was composed of his own Campbell regiment, eight companies of Lowland foot sent by the government general William Baillie, and a substantial number of Campbell clan levies. They were camped beneath the thirteenth-century walls of Inverlochy Castle, confident that Montrose was pinned far to the north. The Royalist attack at dawn came as a complete shock. Argyll himself, reportedly suffering from a dislocated shoulder, watched the battle from his galley on Loch Linnhe rather than commanding from the field. The rout was comprehensive. The Campbell forces were largely destroyed, and a cairn marking where the MacDonalds finally stopped pursuing and killing the fleeing Campbells still stands in the landscape. The victory secured the cooperation of the Marquess of Huntly, whose Clan Gordon levies made him one of the most powerful nobles in northern Scotland. Historic Scotland designated the battlefield in 2011, recognizing its national significance.