On 29 August 1642, just seven days after King Charles raised his standard at Nottingham, Cromwell mustered his troop of horse at Huntingdon. Even in these small beginnings Cromwell's speed and decisiveness of action is apparent. A fortnight later he was ordered to join the main Parliamentary army under the Earl of Essex at Northampton. The Earl had some experience of war on the continent—but not much, and he had little natural talent. But he was an earl and he was utterly reliable; these two qualities counted for much, especially at a time when the allegiance of many men was uncertain—'they will go with the tide' as Lord Willoughby wrote. Not the solid, pipe-smoking Earl of Essex though. Had he been defeated he might well have been tried and executed for treason; but he was ready to die for the cause. When he went to war he took with him his coffin and winding sheet.

Cromwell's troop was put into Essex's own regiment of horse and so took part in the Battle of Edgehill on 23 October. In this battle two inexperienced armies clashed and the result was utter chaos. Neither side really knew what was happening nor who had won—though naturally both claimed to have gained a victory. King Charles, it is true, was left in command of the field of battle and he was free to march on towards London—but he had been free to do that before the battle anyway. By 12 November he had advanced as far as Brentford, but the next day he was checked by the London trained bands drawn up at Turnham Green. Cromwell's own part in the Edgehill and Turnham Green campaigns remains shrouded in darkness. At Edgehill it seems that he arrived late in the day—indeed he was later accused of deliberately avoiding the battlefield altogether. According to Sir William Dugdale he had gone up into a church steeple to survey the scene with his 'perspective glass' (i.e. telescope). On seeing the rout of the Parliamentary cavalry he decided that discretion was the better part of valour and 'made such hast to be gone, that instead of descending the stairs by which he came up, he swing'd down the Bell-rope and ran away with his troop'. But whatever Cromwell may have done that day everything in his later career makes it clear that he was not a coward.

Though his own part in the battle was probably brief and may have been inglorious, Edgehill was to have a profound effect on Cromwell's thinking. On the Royalist side Prince Rupert had insisted that everything be done in the modern Swedish fashion. This may have done no more than confuse the ill-trained Royalist infantry, but there can be no doubt that it was to revolutionize cavalry warfare in England. Gustavus Adolphus had drawn up his cavalry in only three ranks and taught them to charge right into the enemy lines, keeping close order, and reserving their fire until the last moment, then laying about them with the sword. By adopting these tactics at Edgehill against opponents still wedded to the old-fashioned Dutch methods, Rupert's cavalry scored a devastating success. Cromwell was impressed and from then on was to copy Rupert whenever he had the chance. But it was not just a question of tactics. The Royalist cavalry were mostly gentlemen, accustomed to going hunting on horseback. After Edgehill Cromwell discussed the battle with John Hampden and many years later he recalled this conversation.

At my first going into this engagement I saw our men were beaten at every hand … and I desired him that he would make some additions … of some new regiments; and I told him I would be serviceable to him in bringing such men as I thought had a spirit that would do something in the work. 'Your troopers,' said I, 'are most of them old decayed servingmen and tapsters and such kind of fellows; and,' said I, 'their troopers are gentlemen's sons, younger sons and persons of quality; do you think that the spirits of such base and mean fellows will be ever able to encounter gentlemen that have honour and courage and resolution in them? You must get men of a spirit that is likely to go on as far as gentlemen will do, or else you will be beaten still.' He [Hampden] was a wise and worthy person; and he did think that I talked a good notion but an impracticable one. Truly I told him I could do somewhat in it. I did so … I raised such men as had the fear of God before them, as made some conscience of what they did, and from that day forward … they were never beaten.

In the summer of 1642 Cromwell had secured Cambridgeshire for the Parliamentary cause, but Cambridgeshire could not fight the King on its own; the war, to be waged effectively, had to be waged on a broader canvas. As early as July of that year Parliament had recognized that co-operation between adjacent counties was essential, but this ideal was by no means easy to achieve. The country gentry formed local clans; often passionately devoted to the interests of their own group—the community of the shire—they only rarely and reluctantly looked beyond its borders. When Cromwell's friends and neighbours used the words 'my country', they did not mean England; they meant Cambridgeshire or Huntingdonshire. Yet a war against the King could not be conducted by a number of separate counties, each going its own way, raising its own army and planning its own campaign. Some form of association, some kind of military and political alliance between a block of counties was clearly and urgently needed, but in view of the ingrained parochialism of the country gentry it could hardly be a spontaneous growth. To establish such an association would require hard work and tact, all the more so since the whole point of it was to prepare for war, and this was an alarming and money-consuming course of action which most taxpayers would have preferred to see postponed indefinitely. In this situation the initiative had to come from the centre.

On 20 December 1642 Parliament passed an ordinance for the conjunction of five counties: Norfolk, Suffolk, Cambridgeshire, Hertfordshire and Essex, under the overall command of Lord Grey of Warke. But the local gentry were not in such a hurry as the 'bold and bloody-minded men' who sat at Westminster and for weeks the Eastern Association existed only on paper. In mid-January 1643 Cromwell led a troop of horse from London to Cambridge. On the way he stopped at St Albans to arrest the Royalist sheriff of Hertfordshire—no easy task since the sheriff had the support of a market place crowd and twenty armed troopers had to be sent in to snatch him from their protective care. Once at Cambridge Cromwell began to stir things up. The letters he wrote at this time reveal a sense of urgency which he was determined to communicate to others.

We intreat that you would make all possible speed to have in readiness, against any notice shall be given, a considerable force of Horse and Foot to join with us, to keep any enemy's force from breaking in upon your yet peacable country. For we have certain intelligence that some of Prince Rupert's forces are come as far as Wellingborough in Northamptonshire, and that the Papists in Norfolk are solicited to rise presently upon you.

Under the pressure of this 'certain intelligence' the county committees of Cambridgeshire, Suffolk, Norfolk and Essex arranged a joint meeting at Bury on 9 February. Gradually the Eastern Association began to take shape. In April the joint meetings were transformed into a permanent institution by the establishment of the Cambridge Committee: two members from each of the five counties and one from the City of Norwich. The committee soon ran into financial difficulties and found it hard to exercise much authority over the constituent counties, but at least a start had been made in the task of providing the Association with the backbone of a central administration.

Throughout the spring of 1643 Cromwell buckled down to the work of fortifying and garrisoning Cambridge. He was now a colonel and therefore duty bound to raise and equip a whole regiment. By March he had five troops; by September ten; and by early 1644 fourteen—though the usual number of troops in a regiment was only six. But far more than mere numbers it was the quality of his soldiers that counted. 'A few honest men,' he wrote, 'are better than numbers.' His recruiting policy was described by one of the most famous seventeenth-century Puritans, Richard Baxter.

At his first entrance into the wars, being but a captain of horse, he had special care to get religious men into his troop. These men were of greater understanding than common soldiers, and therefore were apprehensive of the importance and consequence of war … he that taketh the felicity of Church and State to be his end, esteemeth it above his life, and therefore will the sooner lay down his life for it. And men of parts and understanding know how to manage this business, and know that flying is the surest way to death, and that standing to it is the likeliest way to escape, there being many usually that fall in flight for one that falls in valiant fight…. These things 'tis probable Cromwell understood; and that none would be such engaged valiant men as the religious. But yet I conjecture, that at his first choosing such men into his troop, it was the very esteem and love of religious men that principally moved him; and the avoiding of those disorders, mutinous plunderings and grievances of the country … which the debased in armies are commonly guilty of. By this means he indeed sped better than he expected … that troop did prove so valiant, that as far as I could learn they never once ran away before an enemy.

Baxter was a conservative Puritan who disapproved strongly of some of the more radical religious movements which were to develop within the army. In 1643 he was offered the chaplaincy of Cromwell's regiment, but declined it—a decision he was to regret. Years later he wrote that 'these very men that invited me to be their pastor, were the men that afterwards headed much of the army and some of them were the forwardest in all our changes; which made me wish I had gone among them … for then all the fire was in one spark'.

It is clear that one consequence of Cromwell's determination to recruit religious men who were committed to the cause was that he was prepared to choose as officers men of a lower social standing than most of his contemporaries thought proper. In 1645 the Earl of Manchester complained that Cromwell did not pick 'men of estate, but such as were common men, poor and of mean parentage, only he would give them the title of godly, precious men … if you look upon his own regiment of horse, see what a swarm there is of those that call themselves godly; some of them profess they have seen visions and had revelations'. As Cromwell himself put it, when defending the choice of Ralph Margery as captain of his thirteenth troop, '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', and later, 'It had been well that men of honour and birth had entered into these employments, but why do they not appear? Who would have hindered them? But seeing it was so necessary the work must go on, better plain men than none….' A number of plain, godly men like John Lilburne left their positions in Essex's army in order to find a more congenial home in the Eastern Association.

Cromwell's first task was to defend the Association against both internal and external enemies. On 14 March Parliament ordered him to deal with a threatened Royalist rising at Lowestoft—but it had been done even before these instructions can have reached him. His five troops left Cambridge on Sunday 12 March. Next day they 'visited' some Royalist houses near Norwich. On Wednesday, assisted by volunteers from Norwich and Yarmouth, they marched to Lowestoft. They found the road covered by a battery of three guns and a chain drawn across it to keep out the cavalry. Cromwell called upon the town to surrender. Badly overestimating the strength of their position the Royalists refused. Cromwell sent in a party of dragoons. They dismounted, crawled under the chain and advanced upon the guns, waving their pistols menacingly. It was sufficient. The defenders fled; the chain was broken and the troopers rode in. They seized a store of arms and arrested the leading Royalists. One man, Sir John Wentworth, agreed to donate £1000 to Cromwell's war treasury in order to have his offence overlooked. After spending two profitable days in Lowestoft, Cromwell returned to Norwich where he remained until the evening of 19 March. Then, by riding all night, he entered King's Lynn early on Monday morning, seized and disarmed known Royalist sympathizers and captured a small ship with a cargo of arms from Dunkirk. By Wednesday, after a busy ten days, he was back in Cambridge. It was all useful exercise for his rapidly growing regiment of horse.

On 7 April Lord Grey with some 5000 men, the bulk of the Association's forces, left Cambridge to join the main Parliamentary army at the siege of Reading. Cromwell was left behind in command of a small detachment responsible for the defence of the Association's north-west frontier. The chief threat came from the Newark Royalists whose lightning raids into Lincolnshire had caused consternation throughout the whole of the Fen Country. Cromwell moved his troops to Huntingdon and sent a garrison of dragoons to Wisbech. He decided to hold the line of the Ouse and requested the associated counties to find the money to fortify its bridges. But then, observing that the Newarkers were distracted by events elsewhere, Cromwell went over to the attack. On 22 April he occupied Peterborough, where his soldiers ransacked the cathedral. On the twenty-fifth he laid siege to Crowland, a small town well defended both by nature and by one of Cromwell's Royalist cousins. The initial assault was beaten back, but despite the discomforts of a Fenland siege in wet and windy weather, Cromwell's men stuck to it for three days, long enough for the defenders to lose heart and surrender. These gains enabled the Association—soon to be strengthened by the addition of Huntingdonshire—to use the River Nene as its frontier, thus making it virtually immune to attack from the north. While in this area Cromwell paid a visit to his uncle, Sir Oliver, who had retired to Ramsey after the sale of Hinchinbroke. Since Sir Oliver was a Royalist he seized his arms and plate, but at the same time did not forget to doff his cap in the old man's presence.

These local successes meant that Cromwell was called upon to act within the framework of a wider strategy—and to be made ever more forcibly aware of the difficulties involved in persuading local commanders to co-operate effectively. The Lord General, the Earl of Essex, had received intelligence that a convoy of ammunition was on its way from the north to Oxford. He ordered Lord Grey of Groby, the commander of the East Midlands Association, to combine forces with Cromwell and with the Lincolnshire Parliamentarians, under Lord Willoughby and John Hotham, to prevent this vital convoy from getting through to the King. The planned interception never materialized. The convoy reached Oxford safely, its escort plundering Leicestershire and Northamptonshire en route. Cromwell blamed Lord Grey, while the Lincolnshire committee blamed everyone else (including Cromwell). Not until 9 May did Cromwell and the Lincolnshire troops—but not Lord Grey—rendezvous at Sleaford, on the Lincoln-Peterborough road. By then it was too late. But for all that the events of the next few days were to be of great importance in the history of Cromwell's military career. Moving slowly westwards the combined forces came across an enemy force two miles outside Grantham late in the evening of 13 May. For half an hour the two sides exchanged musket fire. Then, seeing that the Royalists were reluctant to advance, Cromwell and his fellow commanders decided at last to take the initiative. 'We came on with our troops a pretty round trot, they standing firm to receive us; and our men charging fiercely upon them, by God's providence they were immediately routed, and ran all away, and we had the execution of them two or three miles.' Thus, on a minor scale, Cromwell had proved to himself and to his men that he could do what Rupert had done at Edgehill. The Lincolnshire troops, however, had performed noticeably less well and so it was decided to retire to Lincoln.

The combined force was soon in action again. Lord Fairfax and his son, Sir Thomas Fairfax, needed help if they were to follow up Sir Thomas' victory at Wakefield on 21 May. This time Lords Grey and Willoughby, John Hotham and Cromwell succeeded in assembling a considerable army—about 6000 men—at Nottingham at the end of the month. But nothing came of the projected march north. While there was still an active Cavalier force at Newark neither the Lincolnshire men nor the East Midlanders were prepared to cross the Humber. As a result the Fairfaxes were routed by Newcastle's overwhelming numbers at the Battle of Adwalton Moor on 30 June.

In the meantime the army at Nottingham had been given a new task. They were to be ready to launch a diversionary raid on Oxford in the event of the Earl of Essex moving south. But any hope of them carrying out this assignment was shattered by the quarrel between John Hotham and the other commanders. When they complained about the ill-discipline of the Lincolnshire troops his reply was that he fought for liberty and expected to enjoy it in all things. During a dispute over oats he turned his cannon on Cromwell. Hotham's behaviour led to doubts about his loyalty to the cause. He was watched and was discovered to be in constant communication with the Cavaliers at Newark. On 18 June Hotham was arrested by Sir John Meldrum, a professional soldier whom Essex had sent to take overall command of the forces at Nottingham. He escaped, however, and fled to Lincoln. From there he wrote to the Speaker of the House protesting his innocence and insisting that he had been ill-used by Cromwell and his officers. In his view they were upstarts with dangerously radical opinions. 'The valour of these men had only yet appeared in their defacing of churches.' Eventually he was re-arrested at Hull while he was trying to arrange its surrender to the Queen. As a result of Hotham's defection the Nottingham army disintegrated. The Lincolnshire troops had ridden off with their commander and other contingents soon followed. As a result a second munitions convoy, and the Queen herself, got safely through to Oxford.

In every quarter the war was going badly for Parliament. In the south west Sir Ralph Hopton and his Cornish infantry were winning victory after victory for the Royalist cause. The north was dominated by the army raised by the Earl of Newcastle. In the centre the King had established his headquarters at Oxford and in the fighting between Reading and Oxford, John Hampden was killed. On 26 July 1643, Rupert took Bristol by storm, thus giving the Royalists a vital centre for the import and manufacture of arms. Both Hopton and Newcastle operated independently of the King; he had no effective control over them and therefore there could be no question of a Royalist Grand Strategy. There was no plan for a three-pronged attack on London in 1643. Nonetheless on all fronts the Royalists were doing well, while too many of the Parliamentary commanders were obsessed by the needs of local defence.

Throughout these events Cromwell had been an advocate of a more mobile army—a 'running' or a 'flying army' as it was called—and of a longer range of strategy. But then he was lucky. As he himself pointed out in a letter written in June 1643, the Eastern Association's natural river and fen defences were strong; the bulk of its forces could safely be employed away from home. The commanders in Lincolnshire and the Midlands did not have this precious advantage and so, compared with Cromwell, they often appear in an unfavourable light, over-cautious and obstructionist. Not, of course, that Cromwell's men were immune from the general reluctance to travel. Desertion from his forces was ascribed by the Cambridge committee to the 'eronious opinion of our inexperienced country soldiers that they ought not to be drawne or ledd beyond the bounds of the fyve counties'. But Cromwell's main problem was, inevitably, a financial one. Where could he find the money to pay his men before they pawned their weapons and went home? Most of his letters return again and again to this theme.

I beseech you, hasten the supply to us; forget not money. I press not hard, though I do so need that, I assure you, the foot and the dragooners are ready to mutiny. Lay not too much upon the back of a poor gentleman, who desires, without much noise, to lay down his life, and bleed the last drop to serve the Cause and you. I ask not your money for myself, if that were my end and hope (viz. the pay of my place), I would not open my mouth at this time. I desire to deny myself; but others will not be satisfied. I beseech you hasten supplies.

Initially the money for raising and maintaining Cromwell's troops, like the rest of the Association's forces, came from voluntary contributions. In part this was because Parliament did not want to see any of its revenue from taxation diverted away from Essex's main army and in part because men hoped that the war would soon be over. In March 1643 Cromwell wrote optimistically 'one month's pay may prove all your trouble'. But the effect of this system was to throw all the burden on the shoulders of a few keen Parliamentarians while those who were lukewarm or indifferent escaped lightly. In May, after much prodding from the Cambridge committee, the House of Commons passed the Ordinance of the Fifth and Twentieth enabling the Association to meet its needs by means of local assessment and taxation. By late summer this new system was in full swing.

In mid-July the Earl of Essex ordered Meldrum and Cromwell to meet him at Stony Stratford to prepare for an attack on Oxford. But now it was Cromwell's turn to feel, and submit to, the pressure of local needs. The Newark Cavaliers had seized Stamford and were advancing towards Peterborough. Of itself this was not a very serious threat to the Association's frontier defences; in Cromwell's opinion two or three hundred men could hold the line. What was alarming, however, was the news that the Earl of Newcastle's army was on the march, and might soon engulf the small force with which Lord Willoughby was holding Gainsborough. At once Meldrum turned north, towards Gainsborough, while Cromwell cleared the Cavaliers out of Stamford, giving them no time to fortify the town. They retreated to a nearby mansion, Burghley House, the home of the Earl of Exeter, and were confident enough to reject Cromwell's offer of terms. On 24 July, after a short artillery bombardment, Cromwell ordered his musketeers to storm the house. As they broke in, the Cavaliers, seeing that all was lost, decided that they would, after all, prefer to be granted quarter and Cromwell was generous enough to give it them. Sending several hundred prisoners to Cambridge he then hurried on with his cavalry in order to catch up with Meldrum. They met a Lincolnshire force at a rendezvous at North Scarle on 27 July.

At 2 a.m. next day they moved off in the direction of Gainsborough where Willoughby was besieged by Newcastle's younger brother, Lord Cavendish. In the van of the relieving army rode the Lincolnshire troops, then came the Midlanders, while Cromwell's regiment brought up the rear—in all twenty troops of horse and four of dragoons. As they approached the town Cavendish drew up his men on a steep hill overlooking the road. Despite the strength of the enemy's position Cromwell and his fellow commanders had no choice but to attack it, or leave Willoughby to his fate. The Lincolnshire men led a charge up the hill, brushing aside some opposition. Once at the top they tried to get into battle order, but what with the confusion of the ascent and the difficult ground—it was studded with rabbit-holes—they were still in disarray when the main body of the enemy advanced towards them. With Cromwell now in command of the right wing they met this advance with a charge of their own. So, in Cromwell's words, 'we came up horse to horse, where we disputed it with our swords and pistols a pretty time, all keeping close order, so that no one could break the other'. Eventually, however, the Royalists began to give ground. At once the pressure on them was increased until they turned in flight and were pursued for five miles or so. But Cavendish had kept one regiment in reserve and with this he attacked the four Lincolnshire troops which had not joined in the pleasure of the chase. Cromwell himself seems to have been among the pursuers, but this did not prevent him from seeing what was happening. Seeing was one thing, doing something about it, another. The cavalry commander has no harder task than controlling a charge once it has been launched. Rupert had been unable to do this at Edgehill and, as a result, had not returned in time to take further part in the battle. But this is precisely what Cromwell now managed to do. With the help of Major Whalley, and 'with much ado'—these three little words appear in the narrative letter written by the officers in command of the Lincolnshire forces—he succeeded in regaining control over three of his troops. They hurried back to the scene of the action where Cavendish's reserve appeared to have won the day. What happened there can best be left in Cromwell's own words.

I immediately fell upon his rear with my three troops, who did so astonish him, that he gave over the chase [of the Lincolnshire troops] and would fain have delivered himself from me, but I pressing on forced them down a hill, having good execution of them, and below the hill, drove the General [Cavendish] with some of his soldiers into a quagmire, where my captain-lieutenant slew him with a thrust under his short ribs.

The victors then set about the job of sending supplies of ammunition and powder into Gainsborough in anticipation of the renewed siege it would have to endure when Newcastle's main army came up. But the jubilant commanders were in for an unpleasant shock. Here, once again, are Cromwell's words.

Word was brought us that the enemy had about six troops of horse, and 300 foot, a little on the other side of the town. Upon this we drew musketeers out of the town and with our body of horse marched towards them. We saw two troops towards the mill, which my men drove down into a little village at the bottom of the hill. When we came with our horse to the top of that hill we saw in the bottom a whole regiment of foot, after that another and another and, as some counted, about fifty colours of foot, with a great body of horse.

Newcastle's army was already there. Brilliant as Cromwell's action at Gainsborough had been, it had come too late to save the town.

Worse still the relieving army was itself now in danger of being destroyed. The foot retreated, in panic and disorder, back into Gainsborough, where they were as good as lost. Cromwell had no choice but to return as quickly as possible to Lincoln—no easy task when both his men and horses were exhausted after the day's fighting and were opposed by fresh forces in overwhelming strength. Yet they managed it. Four troops of Cromwell's regiment under Major Whalley and four Lincoln troops under Captain Ayscough took it in turns to stand and face the enemy in order to cover the retreat of the main body. On eight or nine separate occasions a handful of men held the Royalists at bay while their comrades withdrew to safety. It was superbly done, without loss, a retreat, as Cromwell wrote 'equal to any of late times, and the honour of it belonged to Major Whalley and Captain Ayscough, next under God'. Strategically the action at Gainsborough had achieved nothing. The whole of Lincolnshire was soon lost and Cromwell himself withdrew to Peterborough and Spalding, hoping to hold the line of the Nene. But in terms of Cromwell's own career its significance is this. With less than a year's experience of war he had already shown that he could master the two toughest problems facing a cavalry commander: how to keep control of a successful charge, and how to retreat when in a hopeless situation. Two things made this possible. Firstly he taught his troops to charge at 'a pretty round trot'—whereas the Cavaliers always seem to have been in too much of a hurry. Secondly the morale and self-discipline of Cromwell's men was second to none. They could resist the temptation to chase after plunder and easy pickings. 'Truly,' wrote Cromwell, I think that he who prays and preaches best will fight best.' By choosing and training his own men he achieved a degree of control over his cavalry which no other leader could equal. Prince Rupert could not—his Cavaliers did not take kindly to this kind of restraint—while Sir William Waller described his horse as 'such rascals as he could never rule them'.

In the summer of 1643 the testing time came to the Eastern Association. Its very existence hung in the balance. In August, in expectation of Newcastle's triumphant march into East Anglia, Royalist elements in King's Lynn took over the town. Cromwell doubled and re-doubled his efforts to raise men and money. His letters of this period are full of a sense of crisis. 'It's no longer disputing, but [get] out instantly all you can. Raise all your bands; send them to Huntingdon; get up what volunteers you can; hasten your horses.' Or again, 'Lord Newcastle will advance into your bowels; his army is powerful. Better join when others will join and can join with you, than stay till all be lost; hasten to our help.' It was during these terrible weeks that Cromwell began to recruit officers whose low social status alarmed some of the more conservative members of the local aristocracy. The captains of his first five troops had all been closely related to him by blood or marriage. Now the time had come to discard such conventions. As he wrote, 'You see the necessity of going out of our old pace.' …