In 1620 Essex embarked on what was to be an undistinguished military career prior to the start of the First English Civil War. Between 1620 and 1624 he served in Protestant armies in Germany and the Low Countries. In 1620 he joined Sir Horace Vere's expedition to defend the Palatine. In 1621 he served with Prince Maurice of Nassau, in 1622 with Count Ernst von Mansfeld (battle of Fleurus, 29 August 1622). In 1624 he commanded a regiment in the unsuccessful campaign to relieve the siege of Breda.