Aboyne was a member of the powerful Gordon family, who were notable for their Roman Catholic sympathies in a kingdom where supporters of the Protestant Reformation controlled the central government.
The teenage general suffered two reverses in June 1639 at Megray Hill and Brig o' Dee, attributed to unsteady infantry and dissent between his officers, but his losses were light, and his cavalry performed credibly, remaining in the field until they learned that the king had made peace with the Covenanters.
In this short campaign, the Gordon cavalry anticipated the tactics of the English Civil War: they often moved as a mounted column without infantry support, and they usually charged with the sword, discovering how ineffective a pistol caracole could be at Megray.
Unusually, it seems that Aboyne's elite troop of one hundred "gentleman volunteer cuirassiers" were clad in full armour, in contrast to the buff coats and breastplate now favored by most cavalry regiments.
Aboyne now worked hard to arrange a military alliance with Clan Donald and the Irish Confederates, and came to be associated politically with the Scottish earls of Nithsdale, Crawford and Airlie - all open or suspected Catholics.
But Aboyne also found common cause with his former opponent Montrose, a loyal royalist as well as a committed Presbyterian; both of them believed the Scottish Covenanters were now likely to enter the war on Parliament's side.
The next spring, he returned to Scotland, fighting in Montrose's victories at Auldearn, Alford, and at Kilsyth; in each battle, he led a flanking charge on the left wing that broke the Covenanters' right.