The regiment remained in camp most of the winter, drilling and procuring arms, horses and equipment for active service. The men suffered greatly from the exposure of camp life during the severe weather, which caused a great amount of sickness. Toward the last of February the regiment was sent to St. Louis, soon after to Rolla and from there to Springfield. Here the men were furnished a variety of antiquated arms, at which they were justly indignant. The regiment joined the army of General Curtis, which began an invasion of Arkansas and was assigned to General Vandever ‘s Brigade. After a long march the army turned eastward and finally reached Helena on the 15th of July. The Fourth Cavalry followed the fortunes of the army, which had seen more hard marching than fighting. From this time until April 1863, the regiment remained in Helena, employed in scouting and picket duty, having frequent skirmishes with the enemy in the vicinity and losing a number of men. On the 11th of October Major Ben Rector with a detachment of fifty men was attacked and routed. He was captured with fourteen men, while several more were killed and wounded. Lieutenant Parsons with fifty men came up a few minutes later driving the enemy from the field and capturing the lieutenant-colonel commanding.

Colonel Porter was a slack disciplinarian, while Lieutenant-Colonel Drummond was a born soldier and knew the value of strict discipline and rigid drill. Their ideas of military requirements were so radically different that frequent misunderstandings ensued. Drummond resigned and returned to his place in the regular army in June, 1862, while Colonel Porter left his command, returned home without leave, sent in his resignation in March, 1863; he was however dismissed from the service by order of the President. He was the only Iowa colonel thus dismissed during the war. He had previously served as major of the First Iowa Infantry, made a good officer, and had distinguished himself at the Battle of Wilson’s Creek. In July, Major E. F. Winslow was promoted to colonel of the regiment. In January, 1863, Major Ben Rector who had been exchanged and returned to the regiment, died at Helena and in February Captain Tullis died at the same place.

On the 29th of April the regiment moved to join Grant’s army then engaged in the Vicksburg campaign and was assigned to Sherman’s Corps and at once placed in the advance. On the 16th of May it was employed in the rear guard on the march of Sherman’s Corps toward Vicksburg. During the entire siege the regiment was in action being in the saddle fifty-two days out of the fifty-six. The men were worn out by hard and continuous service, many were prostrated by sickness and a large number died. On the 22nd of June, while a detachment from the regiment was blockading the road leading to Johnston’s army then trying to break the blockade, it was suddenly assailed by a body of eight hundred cavalry which cut off one company and made a furious attack on the others. The detachment made a vigorous fight and cut its way through to the camp but with the loss of nearly half its men. On the 5th, after the fall of Vicksburg, the regiment under Colonel Winslow, in a brigade commanded by Colonel Bussey, crossed the Big Black River and took the advance on the road to Jackson. Three hundred men under Major Parkell forming part of a force of eight hundred cavalry commanded by Colonel Winslow, on the 10th of August made a raid of over three hundred miles by Grenada and Coldwater to Memphis. From this time until December the regiment was employed on various expeditions over a wide range of country, losing but few men. The opening of winter found the regiment at Vicksburg in comfortable quarters. By the 19th of December enough reenlistments had been secured to constitute the Fourth Iowa a veteran regiment and during the early part of the winter enough recruits were received to fill up the ranks.

On the 1st of February the Fourth Iowa Cavalry started with Sherman’s army on the Meridian expedition. This, with three other regiments of cavalry under Colonel Winslow, constituted the advance of the army and was almost constantly engaged with the enemy during the entire march of one hundred and fifty miles to Meridian. Battles of more or less magnitude were fought by the cavalry at Bolton, Jackson, Hillsboro, Morton, Tunnel Hill and Meridian. Upon its return to Vicksburg the regiment was granted a long expected furlough. On the 29th of April the veterans were back in camp at Memphis where they were joined by recruits filling up the ranks to the number of 1,350 men.

The Fourth was in the army under General Sturgis in his disastrous Mississippi campaign that marched in June to find General Forrest’s army. Lieutenant W. F. Scott gives the following graphic description of the Battle of Guntown:

"General Sturgis’ army consisted of about twelve thousand men. The cavalry, numbering three thousand, was under command of General B. H. Grierson. Colonel Winslow, of Iowa, had command of a brigade consisting of the Third and Fourth Iowa, and the Tenth Missouri. The cavalry kept in advance of the army, and on the morning of the 10th of June became engaged with the enemy’s cavalry near Guntown, a small station on the Mobile and Ohio Railroad. The Rebels fell back until they gained the protection of their main body, which was soon found to be posted in force and ready for battle. Our infantry was over five or six miles in the rear. General Sturgis ordered it up on the double-quick, on learning the disposition of the enemy, and directed the cavalry to engage him until the infantry should arrive. The enemy, under Forrest, was about equal to our force and was strongly posted on the crest of a semi-circular hill or ridge, in front of which ran a small creek with but one bridge and otherwise impassable, except in a very few places for footmen. The day was very warm and when the infantry regiments came up they were exhausted and disordered, having double-quicked the whole distance from where they were ordered forward. By another great blunder close up with them came the train of more than two hundred wagons, which was hurried across the bridge and parked in a field within easy range and sight of the enemy’s batteries. If there was a time when the attacking force should be well organized and disposed with particular skill it should be when the enemy has so great advantage in position. But in this instance the infantry, tired and disordered, was hurried into the fight, already opened by the cavalry, and was soon and completely beaten. The division, brigade and subordinate officers made strenuous efforts to check the tide of defeat, but without avail, and the whole army was soon in full retreat, the greater part in utter confusion. The Rebels rejoicing in their easy victory pursued with unrelenting vigor, capturing the entire wagon train and cutting off our weary infantrymen in large numbers. It was some time before an attempt at order in the retreat was made, and then Colonel Winslow’s brigade was ordered to act as rear guard, it being the only organized force in the whole command. Of the First Brigade of cavalry a large part had been taken as an escort for the commanding general, while several detachments had been used for other purposes. No attempt was made to restore order in the infantry, and it was hurried along, a fleeing mob. Back toward Memphis fled the disordered army, its retreat covered by Winslow’s brigade of cavalry during the terrible night’s march of June 10th, and through the next day until Ripley was reached. Here the enemy pressed so hard that the running skirmish swelled into a sharp engagement, checking the ardor of the pursuit. General Sturgis made no attempt to reorganize or control the troops after the retreat began and he alone should be held directly responsible for this great disaster. Our losses were about four thousand men killed, wounded and missing, the entire train of two hundred and fifty wagons captured and almost the whole ambulance train with every gun except two belonging to Winslow’s brigade of cavalry were lost."

The Fourth Cavalry was with General A. J. Smith in his Tupelo campaign, also in his expedition sent from Memphis, in the month of August into Mississippi. It was with the army sent into Arkansas the latter part of August in pursuit of Price, which did not overtake him. The regiment was with General Pleasanton in his pursuit of Price in western Missouri taking part in engagements near Independence and at Big Blue River. In forcing a passage of this river Colonel Winslow’s Brigade had a sharp skirmish with the enemy strongly posted on its banks. In this battle the colonel was severely wounded and the Fourth lost several men. At Mine Creek the Union army again overtook Price where a cavalry battle took place on the open prairie. The Fourth Iowa made a most gallant charge on the enemy’s lines breaking through them and sending him off in full retreat. Our whole line now joined in the charge and the rout of the foe was complete. Our army captured nine hundred prisoners, killed and wounded more than three hundred and took seven pieces of artillery. The pursuit of Price’s army was continued until it was driven into the Indian Territory and nearly destroyed. Winslow’s Brigade now returned to St. Louis. It had marched nearly 2,500 miles in three months, worn out two sets of horses and fought in many engagements with unvarying success. The Fourth Iowa took part in the two great raids under Grierson and Wilson, described in another place. In the Battle of Columbus, under Wilson, the Fourth captured nine hundred and forty prisoners and twelve field pieces. In August, 1865, the regiment was finally mustered out of service at Atlanta, Georgia.