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His soldiering was ruthless, brilliant, and backed by faith.

At the outbreak of the English Civil War in 1642 an unheralded military genius was waiting in the wings. Oliver Cromwell, already past 40 years old when he first took up arms, approached the conflict with few preconceptions, instead bringing an uncluttered pragmatism and a religious zealotry to his battle strategy. These traits—along with strong powers of observation, a unique hold on men’s hearts, and an approach to recruiting, training, and organization that placed a premium on battlefield success—combined to make him perhaps the foremost general of the age, and to many the most hated.

Cromwell was born in 1599 to a family of lesser gentry at Huntingdon, in southeastern England. When he was 18, his father died, leaving him to care for his mother and seven sisters. For the next 20 years, those obligations and his own growing family pushed him to the edge of poverty. During that same period, he became a member of Parliament and an ardent follower of Puritanism, among the growing religious sects that had emerged after Henry VIII’s break with the Catholic Church a hundred years before. That break had spawned a century of religious wars across Europe, shredding English society and the international polity of the era.

In 1625 Charles I assumed the throne and within a few years was tangling with Parliament over taxation and religious policies. By 1640 his troubles had escalated into open conflict, and in January 1642 he stormed Parliament with 400 soldiers, set on arresting for treason five of its most troublesome members, including Cromwell. Forewarned, the MPs escaped, and Charles, fearing retaliation, fled north with a few supporters. The stage was set for civil war, as both sides began gathering their forces.

It was onto this stage that Oliver Cromwell stepped. He returned to his home territory and by the following autumn had raised a cavalry troop to fight on the side of the Parliamentarians. He apparently arrived late to the first major battle, at Edge Hill on October 23, 1642. It was a long and bloody affair, with the amateur armies pushing and shoving at each other. Charles commanded the Royalists, while the passive and militarily incompetent Earl of Essex commanded the Parliamentarian army. Only when Prince Rupert of the Rhine, the king’s nephew and the outstanding Royalist commander of the war, unleashed his massed cavalry did the tide turn in favor of the king. But Charles was denied a decisive victory because his undisciplined horsemen rode off in pursuit of the broken enemy cavalry rather than reforming and smashing into the rear of the wavering Parliamentarian infantry.

Though Cromwell had played little part in the fighting, he absorbed two crucial lessons from the confusion: That cavalry, with its speed and shock effect, was now the dominant battlefield arm; and that massed cavalry by itself was insufficient. Victory demanded a highly disciplined force, capable of striking hard, reforming, and striking again.

Returning home, Cromwell began recruiting a full regiment of cavalry that was soon incorporated into one of the Parliamentarian armies known as the Eastern Association. Given tremendous autonomy in the raising and training of his regiment, Cromwell looked for men of strong religious beliefs, who were well respected within their communities regardless of whether they were born to privilege. He selected officers on perceived merit and advanced these men only after they had demonstrated courage in battle and a high capacity to lead men. Parliamentarians like Cromwell’s commander, the Earl of Manchester, looked askance at these officers who were not “gentlemen.” But Cromwell was undaunted: “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…a few honest men are better than numbers….If you choose godly honest men to be captains of horse, honest men will follow them.”

Although his Puritanism and his loyalty to Parliament’s political program were paramount, Cromwell also believed in hard training. He drilled his cavalry on attack techniques— both en masse and by squadron—always knee to knee so as to maintain the unit’s integrity and multiply its shock value in combat. Part of this training focused on preparing broken squadrons to reform and strike again. Even more crucial, victorious regiments were taught to resist the urge for headlong pursuit of a fleeing foe in favor of regrouping for further efforts on a still contested battlefield.

Within a remarkably short time Cromwell’s regiment, eventually called “Ironsides” after Cromwell’s own sobriquet, became the elite formation in the Parliamentarians’ fighting force and later provided a replicable prototype for other units in their New Model Army.

Cromwell’s chance to prove his regiment’s worth was not long in coming. A series of tactical successes in the spring and fall of 1643 gained him notoriety but did little to alleviate Parliament’s mismanagement of the wider strategic effort. The crucial port of Bristol was lost to the Royalists, as was most of Yorkshire. The military incapacity of Parliamentarian commanders, coupled with the tactical brilliance of Prince Rupert, initially gave the king the upper hand. But in September 1643 the Parliamentarian commander, the Earl of Essex, forced Charles to raise the siege of Gloucester, then during the king’s return to London inflicted a sharp reverse on his army at the First Battle of Newbury. It was the one bright spot on Essex’s mediocre military record. The following month Manchester’s Eastern Association advanced north to relieve the besieged forces of Sir Thomas—“Black Tom”—Fairfax at Hull. As the relieving army approached, Fairfax slipped out of Hull with a large force of cavalry and joined Cromwell. Their combined troops mauled a Royalist cavalry force at Winceby and heralded the war’s most fruitful military partnership. The rise in Parliamentarian fortunes induced the Scots to reenter the war, and in early 1644 Cromwell and Fairfax joined with a Scottish invasion force besieging York—the key to northern England.

Rupert’s swift march north and over the Pennines thwarted Parliamentarian hopes. He outmaneuvered the besieging army, relieved York, and joined his force with the king’s northern Royalist army. For the moment Charles’s hold on the north was secure, and though the south was still in jeopardy, Rupert turned his attention to the Parliamentarian forces that had retreated from York to Marston Moor, five miles away.

On July 2 his 18,000 men found themselves staring across a field at 28,000 Parliamentarians. Yet neither side attempted to close for a decisive fight. At about six that evening Rupert concluded no fighting would occur until morning. When he retired from the field for dinner, his Royalist troops relaxed, and their tight formations loosened. Sensing an opening, the Scottish commander, the Earl of Leven, ordered a charge. For a little while, the Parliamentarians prevailed, but a devastating countercharge by a hastily returned Rupert at the head of his veteran cavalry checked their advance. Even Cromwell’s magnificent cavalry was, for a time, hard pressed. As one participant later related: “Cromwell’s own division had a hard pull of it, for they were charged by Rupert’s bravest men both in flank and front. They stood at swords’ point a pretty while, hacking on another; but at last (it so pleased God) he [Cromwell] broke through them, scattering them before him like dust.”

In the center and on the other flank, however, the Parliamentarians were getting the worst of it and all looked lost. Then Cromwell’s recruiting and training program proved its worth. Rather than engaging in a pell-mell pursuit of Rupert’s fleeing horsemen, the Ironsides dispatched a small force to see that Rupert did not return, then reformed, wheeled to the right, and charged into the rear of the Royalist cavalry fighting on the other flank. Next it turned on the infantry regiments in the center. Here the fighting was long and vicious, because the white-clad Royalist elite known as the Lambs chose annihilation over surrender. The results of the battle are best summed up by Cromwell himself: “We drove the entire cavalry of the Prince off the field. God made them as stubble to our swords. Then we took their regiments of foot with our cavalry and overthrew all that we encountered.”

Rupert’s army was destroyed, the north was secure, and Essex had the king trapped in the south. Then, inexplicably, Essex and Manchester gave Charles a reprieve. Instead of finishing him off in central England, Essex marched his army to distant Cornwall, where it met with a series of bloody reverses. For his part, Manchester, believing that his army was exhausted after Marston Moor and the siege of York, took his Eastern Association forces back south again. There he sat for a long while, refusing to budge. After much prodding from Parliament, both commanders eventually marched to join forces with the Southern Association, under Sir William Waller. On October 27, 1644, the combined force of nearly 20,000 men met Charles, who had less than half that number, at the Second Battle of Newbury. Again, the Parliamentarians had a chance to destroy the king’s army but threw it away by failing to press their advantage and then neglecting to block Charles’s only path of retreat.

Cromwell was flabbergasted when he heard Manchester explain his failure to exterminate the king’s army at Newbury: “If we fight 100 times and beat him 99 he will be King still, but if he beats us but once, or the last time, we shall be hanged, we shall lose our estates, and our posterities be undone.”

“My Lord,” Cromwell replied, “if this be so, why did we take up arms at first. This is against fighting ever hereafter. If so, let us make peace be it never so base.”

Fed up with the poor performance of its senior commanders—and with Cromwell leveling verbal attacks on his military superior, Manchester—the House of Commons pushed through the “Self-denying Ordinance” in 1645. It prohibited a sitting member in either house of Parliament to hold an army commission. As there was no mechanism for opting out of the peerage and thus the House of Lords, both Essex and Manchester were forced to resign their commissions. A member of the House of Commons, such as Cromwell, had the option of giving up either his seat or his military position—though a choice was unnecessary in Cromwell’s case, since the Commons, knowing his value, voted him an exception.

Parliament also recognized the inherent deficiencies in the way its scattered forces were organized. Too many of them, such as the Eastern Association and the defenders of London, were only interested in fighting within their own areas. Many others had not made the leap from amateur rabble to professional fighting force. To cure these ills, Parliament took the best regiments from around the country, filled them with the strongest recruits available, and placed England’s leading soldier—Black Tom Fairfax—at their head. Fairfax made Cromwell his second in command and gave him control of the Parliamentarian cavalry. Thus was the New Model Army born. Such a force had never been seen in England before, and on the Continent only Gustavus Adolphus’s Swedish army had rivaled it.

Well trained, well provisioned, and supremely dedicated to its cause, the New Model Army comprised 22,000 men, assembled in 11 regiments of cavalry (6,600), 12 regiments of infantry (14,400), and 1 regiment of dragoons (1,000)—all recruited and trained along the lines of Cromwell’s Ironsides. Their commanders had only one thing to recommend them—battlefield competence. Morale ran high in the New Model Army as it marched north in late spring 1645, spoiling for a fight.

Fairfax hoped to catch and smash Charles’s army before it could link up with a large Scottish force that had remained loyal to the crown. On June 13 Henry Ireton, who would become Cromwell’s son-in-law, defeated a small Royalist force at Naseby, alerting the Royalists to the fact that the New Model Army was just a few miles from their position. Charles was left with two unpleasant choices: To fight against a force of Parliament’s professional veterans, who outnumbered his Royalists, or retreat with an army snapping at his heels. Fearing a collapse of his army’s morale in a retreat, Charles opted to fight.

At 10 o’clock on the morning of June 14, Rupert’s forces charged into Ireton’s troopers. Surprisingly, the Parliamentarians broke on impact. Then, proving that he had failed to absorb the one great tactical lesson of the war, Rupert led his men off the battlefield in pursuit of Ireton’s troopers. As Rupert rode off toward Naseby, two miles away, Cromwell, on the opposite flank, easily defeated a separate Royalist cavalry charge. Unlike Rupert, Cromwell kept his men in hand, swinging them in a great arc into the rear of the Royalist infantry. Already hard pressed by Fairfax’s well-drilled infantry, the Royalist force cracked. Most of the troops ran to the rear, pursued for many miles by Cromwell’s cavalry, who did not let up on the butchery until nightfall. A few regiments, most notably Rupert’s “bluecoats,” held their formations until many were cut to pieces. Seeing that all was lost, Charles tried to lead his Life Guard cavalry in a desperate charge. At the last moment, though, a Scottish nobleman grabbed his bridle and swore, “Will you go upon your death?” Witnessing this, the Life Guard cavalry too lost heart and retreated in disorder. Later, Prince Rupert rallied his surviving men and returned to the battlefield, but when he saw that he was too late, he and his troopers rode off.

The main Royal army was shattered. Over the next several months of 1645 the New Model Army swept through the west of England, capturing the last Royalist outposts and bringing to heel whatever forces the king still possessed. With his options limited, Charles chose to surrender to the Scots in the spring of 1646. After long negotiations, the Scots turned him over to Parliament, and he was placed under house arrest.

This closed what became known as the First Civil War, but it did not end the political or religious turmoil. Failure to reconcile the many grievances that had been papered over during the war kept the embers of conflict glowing. In 1647 Charles escaped and formed an alliance with Scotland. Their joint invasion of England ignited a second conflagration. This time, however, the political winds had shifted, and there were tremendous forces arrayed against Parliament and its guardian—the New Model Army. Winston Churchill later summed up the situation and the result: “King, Lords, and Commons, landlords, and merchants, the City and the countryside, bishops and presbyters, the Scottish Army, the Welsh people, and the English Fleet now all turned against the New Model Army. The Army beat the lot.”

For months the army marched, fought, and marched again— first into Wales then toward the Scottish border. Cromwell’s troops destroyed any force that opposed them. Where Cromwell could not be, small detachments sufficed. Before the year was done, it was over. Again from Churchill: “Cromwell was dictator. The Royalists were crushed; Parliament was a tool, the Constitution was a figment, the Scots were rebuffed, the Welsh back in their mountains, the Fleet was reorganized, London overawed, King Charles….left to pay the bill. It was mortal.” As to the success of the New Model Army, it was “a triumph of twenty-thousand resolute, ruthless, disciplined, military fanatics, over all that England has ever willed or ever wished.” Their ruthless mood did not spare Charles. In January 1649 he was tried and convicted of treason then hanged for his crimes.

With England at his feet, Cromwell turned his attention to Ireland. During the long years of the English Civil War, the Irish had broken free of English control. In fact, only Dublin and Londonderry, both supplied by sea, remained in Parliamentarian hands. Outside Dublin stood the forces of the Irish Catholic Confederation commanded by the Earl of Ormonde, intent on capturing the city before the New Model Army arrived.

On August 2, 1649, the Dublin commander, Colonel Michael Jones, launched a surprise attack on Ormonde’s deploying besiegers and routed them. By the time Cromwell began landing two weeks later, the forces of the Irish Catholic Confederation were retreating in disarray. Cromwell had with him the best regiments in the New Model Army and was looking for a quick fight and rapid conclusion to the campaign. Ormonde, however, had no stomach for testing his still shaken army in the field. So, with few choices left to him, he placed his army within various fortifications throughout northern Ireland, hoping that starvation and disease—the great killers of besieging armies—would do their work. What he had not taken into account was the proficiency the New Model Army, with its vast array of artillery, had in shattering walls.

On September 9 Cromwell aimed his huge 48-pounders at the walls of strongly fortified Drogheda and within days had created two “reasonable breaches.” By the laws of warfare of that time, once there was a reasonable breach, defenders could surrender on terms. By failing to do so, they forfeited all rights to quarter or mercy. Drogheda opted to fight on, forcing Cromwell to order it taken by storm. The ensuing massacre, while not severe by the standards of the era, horrified the Irish, and remains a blight on Anglo-Irish relations to this day. As Cromwell’s dispatch recorded: “Being in the heat of action, I forbade them [his forces] to spare any who were in arms within the town, and I think that night they put to the sword about 2,000 men.”

The actual slaughter was likely over 3,000 and included many women, children, and priests. As Cromwell saw it, though, such ruthlessness was justified: “I am persuaded that this is a righteous judgment of God on these barbarous wretches, who have imbrued their hands with so much innocent blood, and that it will prevent the effusion of blood for the future, which are satisfactory grounds for such actions.”

A similar atrocity befell Wexford in early October, when the 2,000-man garrison, as well as 1,500 civilians, were massacred. The twin atrocities had their effect, as garrisons all through southern and eastern Ireland either fled or surrendered without a fight.

The following spring of 1650 Cromwell began his blitzkrieg through central and southern Ireland, intent on finishing off the remnants of the Irish Catholic Confederation’s forces. Only at Clonmel, held by a soldier named Hugh O’Neill, who learned his business in the Thirty Years War, did the New Model Army meet with a serious reverse. After breaching the walls, Cromwell’s men crossed the breach without meeting any resistance. They had walked into a trap: Hastily constructed interior defenses penned them in. The storming force was slaugh tered, losing as many as 2,000 men before retreat sounded. During the night the defenders considered it the better part of valor to surrender on terms rather than face the wrath of a fresh assault.

After the fall of Clonmel, Cromwell departed for England, where he was needed to meet a new threat coming out of Scotland. He left his son-in-law Henry Ireton to complete the Irish conquest. In his nine-month campaign, Cromwell had conquered most of Ireland. What Irish forces remained were mostly trapped behind the Shannon River, where they would make determined stands in Limerick and Galway. Eventually, though, organized Irish resistance broke down and the conflict became a merciless guerrilla war. Before it was over, almost half the population had been killed by war, disease, or famine, and another 50,000 were shipped overseas as indentured servants. The subsequent Cromwellian Settlement banned Catholicism and deprived Catholic landowners of their property.

In short, Cromwell did his utmost to destroy Catholic Ireland, with grievous results. Churchill summed them up: “Cromwell’s record was a lasting bane. By an uncompleted process of terror, by an iniquitous land settlement, by the virtual proscription of the Catholic religion, by the bloody deeds already described, he cut new gulfs between the nations and the creeds….The native inhabitants…across three hundred years, have used as their keenest expression of hatred ‘The Curse of Cromwell on you.’”

Even as the ruin of Ireland continued, Cromwell prepared to eliminate a new Scottish threat. Scot- land had proclaimed its support for Charles’s son, Charles II, making him king. After the Scots refused Cromwell’s appeal to them to see the error of their ways and lay down their arms, the New Model Army marched north in May 1650. But this time Cromwell’s forces set forth before they were ready. Without proper supplies and facing stiff resistance from determined Scots led by the competent David Leslie, the army soon bogged down. By the end of August Cromwell’s legendary army was starving, sick, and beginning to come apart. He ordered a retreat toward the seaport at Dunbar, but by then the army had already lost perhaps a third of its original strength to hunger and disease.

At first, Leslie’s Scots followed cautiously. But once the Scots had entrenched themselves on the heights around Dunbar, they were able to observe the vastly outnumbered New Model Army—by all appearances a trapped, weak, and demoralized force, more like a rabble than an army. With rash overconfidence, they left their strong positions on the heights and marched into the valley outside Dunbar. Their likely intent was to press Cromwell’s forces hard enough to force a surrender. What they did not expect was a fight.

But neither Cromwell nor his veterans were much for surrendering. Cornered but still dangerous, they struck out viciously. At dawn on September 3, 1650, Cromwell’s assault went forward. “Now,” he yelled to his soldiers, “let God arise and his enemies be scattered.” Surprised by the attack, the Scottish right, which faced the hardest blow, collapsed in a twinkling. Seeing this, the remainder of the Scottish force ran hastily to the rear, leaving 3,000 dead and another 8,000 as prisoners. In less than an hour the New Model Army had crushed a Scottish army that only a day before had considered itself triumphant.

Rather than demoralize the Scots or Charles II, news of the Dunbar disaster galvanized them. Scotland reacted with fury. A new army was raised with Leslie again in command. This time, however, when the Scots marched south, Charles was with them. It was now winner take all: Charles’s objective was London. Cromwell took the new threat in stride. He could easily have marched the New Model Army into the path of the invasion and brought it to battle. He chose not to. He had no wish to stop the invasion or defeat yet one more Scottish army. Rather, he wanted to draw it deep into England and then annihilate it.

Cromwell caught up with the Scottish army at Worcester. This time he was the one with overwhelming numbers— close to 30,000 against 12,000 Scots. By conducting an early battle of maneuver, which previous English armies had been incapable of, he had also trapped the enemy. When the New Model Army made its final assaults, it came from three sides simultaneously. The result was a foregone conclusion. Still, the Scots fought tenaciously. “The battle was fought with various successes,” Cromwell reported, “and in the end became an absolute victory and so full a one as proved a total defeat and ruin of the enemy army.”

Charles II had acquitted himself well on the field of battle and had only barely escaped. For weeks he wandered the countryside, enduring multiple hazards before finally making his way back to Paris.

The final shot of the Civil War had been fired. The New Model Army would go on to fight well against the Spanish army, but its time was marked. Cromwell’s “Protectorate” government was never popular and became less so with each passing day. Two years after Cromwell’s death in 1658, Parliament voted that Charles II be restored as king. Upon taking power, Charles did not forget the instrument that had defeated his father and seen him off at Worcester. By royal command he disbanded the New Model Army. The only units allowed to continue were a king’s Life Guards and a remnant of cavalry.

A dozen years later, as war with Netherlands loomed, Charles and England had reason to regret abolishing the best army in Europe. When in 1672 Charles complained to the French ambassador about insults to his country that would never have taken place during Cromwell’s rule, the ambassador replied: “Ha, Sire, that was another time; Cromwell was a great man, and he and his army were feared on land and sea.”


Jim Lacey is professor of strategic studies at the Marine Corps War College. His most recent book, with coauthor Williamson Murray, is Moment of Battle (2013). Sharon Tosi Lacey is a serving army officer currently assigned to the Army’s Center for Military History. Her book Pacific Blitzkrieg (2013) was selected as the best operational history of the year by the Army Historical Foundation.

Originally published in the October 2014 issue of Military History Quarterly. To subscribe, click here.