 King James held Colonel Browne's Infantry and Colonel Purcell's Dragoons in reserve at the Battle of the Boyne, and late in the day he committed his reserve behind the Comte de Lauzun, as the latter was about to charge the Williamite right flank which faced him within cannon shot.King James ordered Sir James Carny, the reserve commander, to move the reserve up to Lauzun's right flank and Purcell's Dragoons to dismount and engage as infantry.At this moment an aid rode up with the news that the Irish right flank had been defeated.