In 1636 Arundel undertook an unsuccessful mission to the emperor Ferdinand II to procure the restitution of the Palatinate to the young elector, Charles Louis, the Queen of Bohemia's son.. In 1638 he was entrusted with the charge of the forts on the border with Scotland, and, supporting alone amongst the peers the war against the Scots, was made general of the king's forces in the first Bishops' War, though "he had nothing martial about him but his presence and looks." He was not employed in the second Bishops' War, but in August 1640 was nominated captain general south of the Trent.