Ironside was the name given to a trooper in the Parliamentarian cavalry formed by English political leader Oliver Cromwell in the 17th century, during the English Civil War. The name came from "Old Ironsides", one of Cromwell's nicknames (although it has also been suggested that it was Cromwell who actually derived his nickname from the "Ironsides" he led in battle.)
Cromwell first mustered a troop of cavalry (then referred to as "horse") at Huntingdon in Huntingdonshire, on August 29, 1642, early in the Civil War. After witnessing the defeat of the Parliamentarian horse at the Battle of Edgehill later that year, Cromwell wrote to fellow Parliamentarian leader John Hampden,
"Your troopers are most of them old decayed servingmen and tapsters; and the Royalists troopers are gentlemens' sons, younger sons and persons of quality; do you think that the spirits of such base and mean fellows [as ours] will ever be able to encounter gentlemen that have honour and courage and resolution in them?"
"I had rather have a plain russet-coated captain that knows what he fights for and loves what he knows, than that which you call a gentleman and is nothing else. I honour a gentleman that is so indeed."
By April, 1644, after two years of war, Cromwell's unit had grown into a "double" regiment of no less than 14 troops (of which are listed below). (A regiment normally had only 6 troops). Cromwell by this time was Lieutenant General of the Horse in the Parliamentarian Army of the Eastern Association, and the regiment would be routinely commanded by its Major, Cromwell's cousin Edward Whalley. The regiment unit played a major part in the victory over the Royalists at the Battle of Marston Moor, where the discipline of Cromwell's wing of horse was decisive. Where a victorious wing of Royalist cavalry scattered in search of plunder, Cromwell's men rallied after defeating their immediate opponents, and then swept the disordered Royalist armies from the field.
It was a different story by the time of the Second Battle of Newbury later that year. After the Parliamentary high command of Waller, Manchester, Balfour and Cromwell decided to split their large force into two, Cromwell, the Eastern and London Association Cavalry and the Southern Association headed across the river and toward Donnington Castle in the West. The regiment was part of the first attack on the King's western forces under Goring and Astley, but was beaten back and had to be relieved by his fellow commander, Sir William Balfour, and his London horse. This was anothern great turning point for the Ironsides.
Although the phrase "Ironside" suggests heavily armoured men, Cromwell's troops were equipped in the common style of the day, with armour limited to back- and breastplate and "pot" helmet. It does seem that they presented a uniform appearance which contrasted with that of the Cavalier horse, which became increasingly individual during the war through shortage of equipment or personal choice.
As Puritans, the Ironsides often attributed their glory in battle to God. Their religious beliefs extended to the field where they adhered to strict ethical codes. In quarters, they did not drink or gamble. They did not partake in the traditional spoils of war and did not rape or pillage defeated opponents (although their religious zeal sometimes led them to be merciless to Catholic enemies).
At the Battle of Gainsborough, one of the troop captains, James Berry is debated to have killed the Royalist commander, Sir Charles Cavendish, relation of Sir William, the Marquess of Newcastle (Commander-in-Chief of the Royalist forces in the North); which was on the day of a decisive Parliamentarian victory.