At the beginning of the Civil War, Parliament relied on soldiers recruited by large landowners who supported their cause. In February 1645, Parliament decided to form a new army of professional soldiers and amalgamated the three armies of William Waller, Earl of Essex and Earl of Manchester. This army of 22,000 men became known as the New Model Army. Its commander-in-chief was General Thomas Fairfax, while Oliver Cromwell was put in charge of its cavalry.
Members of the New Model Army received proper military training and by the time they went into battle they were very well-disciplined. In the past, people became officers because they came from powerful and wealthy families. In the New Model Army men were promoted when they showed themselves to be good soldiers. For the first time it became possible for working-class men to become army officers. Oliver Cromwell thought it was very important that soldiers in the New Model Army believed strongly in what they were fighting for. Where possible he recruited men who, like him, held strong Puritan views and the New Model Army went into battle singing psalms, convinced that God was on their side.
The New Model Army took part in its first major battle just outside the village of Naseby in Northamptonshire on 14 June 1645. The battle began when Prince Rupert led a charge against the left wing of the parliamentary cavalry which scattered and Rupert's men then gave chase.
While this was going on Cromwell launched an attack on the left wing of the royalist cavalry. This was also successful and the royalists that survived the initial charge fled from the battlefield. While some of Cromwell's cavalry gave chase, the majority were ordered to attack the now unprotected flanks of the infantry. Charles I was waiting with 1,200 men in reserve. Instead of ordering them forward to help his infantry he decided to retreat. Without support from the cavalry, the royalist infantry realised their task was impossible and surrendered.
By the time Prince Rupert's cavalry returned to the battlefield the fighting had ended. Rupert's cavalry horses were exhausted after their long chase and were not in a fit state to take on Cromwell's cavalry. Rupert had no option but to ride off in search of Charles I.
The battle was a disaster for the king. About 1,000 of his men had been killed, while another 4,500 of his most experienced men had been taken prisoner. The Parliamentary forces were also able to capture the Royalist baggage train that contained his complete stock of guns and ammunition.
The Battle of Naseby was the turning point in the war. After Naseby, Charles was never able to raise another army strong enough to defeat the parliamentary army in a major battle.