Monk had hardly time to weary of his inactivity before a new storm burst in the north. Scotland had taken to herself a covenanted King, and an invasion was resolved upon by the English Parliament. Cromwell was recalled from Ireland, and in June, 1650, to the confusion of the Presbyterian opposition, he was voted to the command of the army. He at once sent for Monk to assist him in the organisation of his forces, and promised him a regiment.

The significance of this it is hard to exaggerate. When we remember how fastidious Cromwell was about the private character of the men he worked with, it cannot but impress us with the extraordinary sense he must have had of his obligations to Monk. The highest military abilities would never have induced him to employ a man who was living in open contempt of the seventh commandment. It was an offence of such gravity at that time that it had been recently made capital. Yet Cromwell was determined his trusty friend should have his reward, and that in spite of the difficulty of finding him a regiment. The command of Bright's, which lay at Alnwick, was vacant, but a dangerous spirit of democracy and autonomy was growing in the army. Bright's had been one of the victorious regiments at Nantwich. They had to be asked if they would accept Monk for colonel, and they refused. "We took him prisoner," they cried, "at Nantwich not long since, and he will betray us," and ominously enough Lambert, with whom the last great struggle was to be, was chosen in his stead. From that moment the two most celebrated of Cromwell's lieutenants were doomed to an incessant rivalry.

But Cromwell was not to be thwarted. As there was no regiment for his friend, he made one. At Newcastle lay Sir Arthur Haslerig's renowned Blue-Coats, and at Berwick was Colonel Fenwick with his newly raised Northumberland regiment. The field-force which had been voted for Cromwell was complete, but in his masterful way he drew five companies from each of these regiments and made up a new one for Monk. Then he laconically informed the House what he had done, and coolly requested that the new regiment should be taken on the establishment and the two weakened garrisons recruited. Like lambs the Government consented, and so in lawless birth, a reward for service that none dared name, began the famous Coldstream Guards.

The staff-appointment which Monk held was that of acting lieutenant-general of the Ordnance. Cromwell would doubtless have preferred to see him sergeant-major-general—an appointment which in those days of amateur soldiering it was usually thought necessary to fill with a soldier of fortune—that as chief of the staff he might supply the technical shortcomings of the commander-in-chief. It was, however, already occupied by Lambert, whose training as a lawyer can hardly have qualified him for the proper discharge of its complex duties. Indeed more than once, in cases of extreme difficulty, we shall see that Monk had to take over his work, and thus intensify the antipathy which marked their relations from the first.

It is impossible here to repeat the oft-told tale of the Dunbar campaign; which is the more to be regretted as Monk's share in it has never been done justice to. Cromwell had excellent reasons for not saying too much about him in despatches; and Hodgson, the other best known authority, being in Lambert's regiment, studiously keeps in the background the rival of his idolised colonel. Yet it is certain that no voice had so much weight with Cromwell as Monk's, and he was consulted at every point. Up to Dunbar, too, the lion's share of the active operations fell upon him. The artillery duels by which it was sought to goad Leslie into an engagement were under his direction, and it was he who took the castles of Colinton and Redhall during Cromwell's attempt to turn the Scotch position before Edinburgh.

During the terrible retreat on Dunbar it is hardly too much to say his consummate technical skill saved the army from destruction. More dead than alive the remnants of Cromwell's splendid force had reached Haddington. Sick, shattered, and harassed to death with incessant marching through the rain and mire, they seemed now an easy prey. About midnight an attack on the rear-guard had been repulsed, but the position was none the less desperate. Leslie was at their heels bent on destroying them before they could reach their ships. He was out-marching them to the right on a line parallel to their own, and it was certain that with the first glimpse of daylight he would be upon them. Yet it seemed impossible to do anything. A Scotch mist was driving across them and the darkness was absolutely impenetrable. As they stood in the ranks the soldiers could hardly see their right and left hand files. Yet Monk undertook to draw the army up in line of battle fronting to its true right. It was Lambert's duty as major-general; and it must have been a rough blow to his vanity that his rival was not only allowed to undertake a task for which his own experience was inadequate, but that he succeeded in what seemed an impossibility. For succeed he did. By feeling or instinct he set about the work, of which we can now have little conception. Complicated mathematical calculations were involved; foot had to be mingled with horse, and pikemen with musketeers. But all this was child's play to Monk. The dismal morning broke, and there Leslie saw facing him a line of battle, perfect in every distance and resting on Gladsmuir and Haddington, with a swollen tributary of the Tyne to protect its front. Without hesitation the Scotch general declined the action, and hurried on to secure Cockburnspath and cut off Cromwell from Berwick.

We must pass on to the evening of September 2nd. In Dunbar the spiritless supper at the headquarters' mess was over and Cromwell was walking with Lambert hoping against hope for a chance of escape. But the position was unchanged. There was still the swollen Brock roaring along its impassable channel in heavy spate from the right to where it joined the sea on the extreme left: there was the narrow stretch of meadow beyond; and then the hills, where dimly in the gathering gloom the Scottish host lay out and penned them in past hope. Suddenly there was a movement. The Scotch were beginning to draw down from the hills, the horse on their right flank were taking ground towards the sea. It was clear Leslie meant to attack on the morrow where on the English left the Berwick road crossed the Brock. The manoeuvre was difficult. In the narrow piece of level ground that was available between the hills and the burn it would take long to execute, and until it was complete the right flank of the Scots which had hitherto been secure in the difficult ground about Cockburnspath was exposed. Leslie must be attacked when his movement was half-done. It was a desperate chance, but the only one against his overwhelming numbers.

Lambert agreed with Cromwell's suggestion, but the General would not decide without Monk's opinion. He was probably busy superintending the embarkation of his heavy guns, but he was quickly found and received the idea favourably. All depended on the success of the first attack. The ford must be seized before Leslie was ready to cross, and then the Scotch line as it lay between the hills and the burn taking ground to the right might be rolled up like a scroll. There must be no thought of repulse; he offered to lead the foot in person, and again he was given the post that Lambert as major-general ought to have filled.

The Council of War was assembled at once, and Monk demonstrated to the colonels the practicability of Cromwell's idea. The attack was decided on, and the first glimmer of dawn saw Monk standing beside the burn, half-pike in hand, at the head of his regiment of foot.6 All was ready to begin, but Lambert, who was to lead the attack at the head of the horse, was away, to Cromwell's annoyance, worrying about Monk's guns with which he had suggested a feint should be made upon the Scots' left. Valuable time was lost, but at last he came, and the horse dashed across the ford followed by Monk in support. A desperate hand-to-hand fight ensued. For an hour the thing hung in a balance. The flower of the Scotch regiments was there, and the resistance they offered was worthy of their reputation. But regiment after regiment poured over from the Dunbar side, ever inclining to the left till the Scotch right was overlapped. All this time Monk was fighting desperately at pike's length with a regiment that would not break. But now as the rout of the out-flanked regiments exposed it to the horse it had to go with the rest, and then the day was won. Galled by the guns and small-shot from across the swollen burn, the Scots' left and centre, incapable of reaching their enemy, would stand no longer. As the beaten right fell back upon them, rolling up the line as they came, a panic ensued. Throwing down their arms they fairly ran, nor stopped till they reached Edinburgh.

The fall of Edinburgh Castle ended the campaign of 1650. Monk had been appointed governor of the city, and with the duties of his office and the preparations for the next campaign he was occupied during the winter. By February, however, in the following year, he was at active work again. Tantallon Castle was his first care, and by the aid of the splendid siege-train he had organised he battered the ancient stronghold of the Douglas into submission in forty-eight hours: Blackness Castle on the Forth followed in March; and thus by the time spring had fairly begun the way was cleared for the real object of the campaign, and Monk's services were rewarded with the substantive rank in which he had been acting.

Leslie during the winter had reorganised his army, and was occupying an intrenched position at Torwood, to the north of Falkirk, covering Stirling. Beyond him the government was being carried on in security at Perth. The Torwood position was far too strong for a direct attack to be risked. Every endeavour to turn it or to tempt Leslie to leave failed, and yet it was imperative that he should be dislodged.

Who suggested the daring manoeuvre by which the end was at last achieved we do not know. At this time Monk was higher in his commander's counsels than ever. Brilliant tactician as he was, Cromwell had hitherto given little evidence of far-sighted strategy. He was not a trained soldier, and Lambert was only a talented civilian like himself. Deane had had no scientific training in the continental school, nor did he join the army till May. Indeed Monk was the only professional soldier on the staff at the time the manoeuvre was projected. But if Cromwell was no professional soldier he had the military instinct too highly developed not to know his own shortcomings, and to appreciate at its full value the consummate technical knowledge of his new adviser. The few words that fell blunt and sure from the taciturn soldier of fortune had more weight in the Council of War than all the rest together. At any rate we may be sure the movement was the result of Cromwell's and Monk's reconnaissance of Leslie's position at Stirling in September, and that it was worked out by Monk on his return to Edinburgh. For in November a requisition went up to the Council of State for the flotilla of flat-bottomed boats which the contemplated operation required.

It was known at the English headquarters that there was a party about the King who were urging an advance into England. The plan had much to recommend it, and Cromwell determined to spoil it by forcing Leslie's hand. A footing was to be secured upon the opposite side of the Forth, and a blow threatened upon Perth. If Leslie attempted to quit his intrenchments to parry it he was to be attacked in his true front, and compelled to reoccupy his position. The English army was then to be thrown suddenly across the Forth, and a dash on Perth developed before he could move again. Thus the Torwood position would be turned, Stirling taken in reverse, and no way would remain of loosing Cromwell's new hold except to attack him on his own ground, or by advancing into England to compel him to follow. In either case the victory was almost a certainty for the Commonwealth. As early as the middle of April part of the flotilla had arrived, and Monk had made an attack on Burntisland. He was repulsed. Cromwell's illness delayed further operations for some time. At the end of June he recovered. Major-General Harrison was sent with all the force that could be spared into Cumberland to check the expected inroad of the Scots, and Cromwell advanced to threaten the position at Torwood. Early in July he moved westward to Glasgow with the double object of securing the affections of the people in that quarter and of drawing Leslie's attention away from the Forth, while the preparations for the descent on the north bank of the river were completed. On July 17th a small party landed at North Ferry, rapidly intrenched themselves, and Lambert followed with a strong division. Cromwell had moved back to his old position before Torwood, and as though a direct attack were still his real object, Monk was ordered to storm an outpost.

All was now ripe, and at the end of July the long contemplated operation was commenced. In the precision with which it was carried out we may at least see Monk's unerring hand. The success was complete. By August 3rd Perth was in the possession of the Commonwealth. Leslie was in full career for the south, and Cromwell and his generals repassing the Forth in hot pursuit.

Yet some one must be left behind. The centre of interest had suddenly shifted, but work in plenty remained. Some one must be left in the post of peril to play Cromwell's part while he was gone; some one who knew how to strike sharp and hard, and could fix a grip of iron on the country before the army that was gathering in the Highlands could replace the one that was gone. Monk was the man, and well he justified the choice.

The force at his command consisted of but four regiments of horse and three of foot, in all less than six thousand men. With this he attacked Stirling, and on the 16th the maiden castle surrendered. For this service he received the thanks of Parliament, and was voted £500 a year in Scotch land for ever.

But the work was only commenced. By the capture of Stirling he had but secured an advanced base from which to operate against the north. The Committee of Estates, to which Charles had entrusted the kingdom before he left, was sitting at Dundee, and organising, in concert with a number of clan-chieftains, a new army for the King. Dundee then was Monk's real objective. No sooner was Stirling in his hands than he hurried forward a small flying column to stop the supplies of the town. Three or four days were spent in disposing of prisoners and booty at Stirling and in setting things in order there, for the most precise strategist of to-day could not be more careful about his base than Monk. Then the general followed with the bulk of the foot and the siege-train.

Just before reaching Dundee he was joined by a body of cavalry under two officers, who were destined to play a prominent part in history. The horse were commanded by Colonel Alured, a daring cavalry leader with red-hot political opinions of an advanced socialistic type, an Anabaptist of the Anabaptists. At the head of the dragoons rode a little fiery man, whom they all adored. It was the famous Colonel Morgan, a soldier of fortune after Monk's own heart, who knew nothing of politics and everything of his profession. They had probably served together the greater part of their lives, and were now at any rate fast friends with unbounded mutual admiration. There was no one to whom Monk would rather commit a piece of difficult work than this little dragoon, and he had arrived in the nick of time.

For Monk, as we have seen, with his advanced ideas of the military art, the Intelligence Department was his chiefest care. "The eyes of an army," to use his own expression, he cherished as his own. Spies as usual had been busy, and now he learned that on his approach the Government had retired to the Highlands and was sitting at Alyth, fourteen miles away, at the edge of the hills, where a force was daily expected to assemble for the relief of Dundee. Monk at once determined on a surprise so daring that it savours more of romance than the deliberate expedient of a wary strategist. Morgan was sent for, and he and Alured were told to take their men, disguised as far as possible and mixed with Scotch deserters, and attend the enemy's rendezvous.

Late on the night of the 27th they marched, and unmolested reached Alyth in the first hours of the morning. To avoid suspicion they boldly marched to the farther side of the town, and there quietly halted as though they were a party of the expected troops. No one interfered, and about three o'clock, after a short rest, when sleep was the deepest, they suddenly broke into the astonished town. Hardly a blow was struck. Old Leslie, the commander-in-chief, was taken in his bed, and the rest of the Government shared his fate; and as Monk went forth to direct his siege-works Alured and Morgan rode into camp with three hundred noblemen, lairds, and ministers prisoners in their train. At one stroke Scotland was as it were beheaded. It was a bloodless victory, as complete almost as the "crowning mercy" at Worcester, now on the eve of being fought. "Truly," wrote Monk in his despatch to Cromwell, "it is a very great mercy which the Lord of Hosts hath been pleased to bestow upon us, observing the time and season. This is the Lord's work, and therefore He alone ought to have the praise." But he concludes by asking for Morgan's promotion. That he could so far have departed from his ordinary style only shows us how great had been the influence of Cromwell's coercive personality upon him.

Still Dundee did not know the extent of the disaster. The garrison could not believe that all hope of relief was at an end, and contemptuously refused Monk's summons. On the third day the batteries opened. All through the last night of August they thundered, and in the morning there was a practicable breach. Monk knew well the garrison was hopelessly demoralised and would be an easy prey, yet he strove to save bloodshed. Twice again he offered them quarter, and twice again they refused. Then at last he gave the word for an assault.

The infantry were very weak from sickness, and the storming parties were strengthened by dismounted troopers and a naval brigade. These elements were not likely to decrease the heat of the fight, and added to this the town was known to contain property of immense value. With incredible fury the breach was carried in one rush. The supports of horse were through almost as soon as the footmen, and a desperate struggle ensued in the streets. In a few minutes it was over and the stormers rushed on wildly through the town hacking down everything in their way. A number of women, and even some children who were in the streets, were borne down in the rush. Soon all that resisted were a party who with the governor had taken refuge in a tower. Preparations were being made to smoke them out, when they asked and received quarter. Unhappily, as the governor was being taken before Monk he was pistolled by a fanatic officer, an outrage which the general seems to have felt as a blot on his own untarnished reputation as a soldier. Resistance was now at an end, but Monk seems to have thought it his duty to give over the town to two days' pillage as a chastisement for its obstinate refusal of quarter.

The remaining garrisons surrendered on terms in rapid succession, and the Highland strongholds were one after another reduced by his officers. He himself took no active part in the operations. The iron constitution on which he drew so recklessly during his long campaigns at length gave way, and a few days after the surrender he was laid up in Dundee with a fever. By January he had sufficiently shaken it off to be able to meet the new Scotch commissioners who had arrived at Dalkeith from London to negotiate the Union, but in February he was compelled to go south for the benefit of his health. It is worthy of note that he started on the journey in the same coach with Lambert, who was also on the commission, but before Berwick was passed they agreed to separate, ostensibly because Monk was too ill to travel fast enough for his rival.

It is said that at this time there was an idea of sending into France ten thousand of those matchless troops of whom all Europe was talking, as was afterwards done under Morgan. For Monk was reserved the superlative honour of commanding them. But the time was not yet ripe, and instead of figuring as leader of the finest soldiers in the world, for so every one then considered them, Monk went quietly down to Bath to mend his shattered health.