In the midst of the Confederate invasion of Maryland, Union Major General Lew Wallace had heard and read the reports of Lt. Gen. Early’s movements in the Shenandoah Valley and Maryland. He asked Lieutenant Colonel David Clendenin to move westward, across the Catoctin Mountain, and locate the Confederate army. From his headquarters near Monocacy Junction, Maj. Gen. Wallace tried to formulate his plan of defense, but found that he needed to size up the situation.
At dawn on July 7, Lt Col. David Clendenin, with 250 troopers of the 8th Illinois Cavalry, moved out of Frederick and marched to the Catoctin Mountain to observe the Confederate activity. Lt. Col. Clendenin was supported by a section of cannon from Captain Frederick Alexander’s Baltimore Battery, under the command of Lieutenant Peter Leary. While the 8th Illinois Cavalry was making their way to the Catoctin Mountain, several miles to the west on South Mountain, the Confederate cavalry was moving along the National Road. They were ordered to scout the area for the preparation of the Confederate army crossing over South Mountain. Confederate Major General Robert Ransom ordered Brigadier General Bradley Johnson to advance cautiously, ensuring that he did not move out of support distance of the main infantry body.
Leading the advance of Brig. Gen. Johnson’s cavalry was Major Harry Gilmor and his battalion of the 2nd Maryland Cavalry. At 10:00 a.m., Major Gilmor made his way through Middletown trotting along the same streets, where in September of 1862, Major General J. E. B. Stuart had fought. Two miles east of Middletown, along the National Road, Major Gilmor was surprised by the sound of cannon fire from Lt. Leary’s command, and a shell hitting seconds later near him, wounding his brother Robert, in the leg.
After taking cover, Major Gilmor began deploying his battalion in the fields. He quickly ordered his men to dismount and prepare for a Union cavalry attack. When no attack was made, Major Gilmor ordered two squadrons forward, but the Confederate troopers stalled as they approached Hollow Creek. Both sides simultaneously fired into each other and the skirmish quickly heated up. Hollow Creek presented a natural barrier, and provided Lt. Col. Clendenin with some much needed protection. Although a small creek flowed under the bridge, the creek bed itself was deep and steep.
Lt. Col. Clendenin ordered his command across the bridge, and quickly deployed his skirmishers. The Union troopers began pushing Major Gilmor’s troops back toward Middletown. Upon seeing Brig. Gen. Johnson’s larger Confederate cavalry, comprised of one thousand men, making its way to the scene of the engagement, the Union cavalrymen halted on the outskirts of the town. Lieutenant Leary saw the Confederate force and fired his two cannon into them. As one of the Union shells hit, the explosion knocked nine 8th Virginia Cavalry troopers off of their horses, killing five of them.
Brigadier General Johnson ordered the 8th Virginia Cavalry forward to support Major Gilmor’s Marylanders. The two units began pushing Lt. Col. Clendenin’s command back, regaining the ground they had lost all the way to Hollow Creek. By 11:00 a.m., the Union troopers were pushed back toward Braddock’s Gap, where Lt. Col. Clendenin quickly reestablished his defensive line covering Braddock’s Gap, supported by Lieutenant Leary’s two cannon.
Lt. Col. Clendenin quickly sent a courier to Maj. Gen. Wallace’s headquarters near Frederick. Major General Wallace had heard the sounds of artillery in the distance. Arriving at his headquarters, the courier handed the dispatch over, which read “Catoctin Pass [Braddock’s Gap], Jul 7 1864.” This short and simple dispatch meant only one thing, that the Confederate army had been located.
As Lt. Col. Clendenin prepared for a counter attack, Major Gilmor’s forces had halted. They were waiting for additional reinforcements from Brig. Gen. Johnson to come up, with artillery support from Griffin’s (three gun) Battery. As Major Gilmor advanced, Brig. Gen. Johnson’s brigade fired upon Leary’s guns that were situated in Braddock’s Gap. As Major Gilmor made his way past Hollow Creek, he quickly halted and waited for support.
Brigadier General Johnson and his cavalry crossed Hollow Creek and deployed. Johnson quickly ordered out two hundred and fifty men to occupy Lt. Col. Clendenin’s front, while he sent two squadrons to the Union flanks. There were very few Union troops to prevent this attack, and the Confederates were going to simply roll them up.
Near noon, Lt. Col. Clendenin, seeing the Confederate movements, fell back to a stronger position off the Catoctin Mountain, a few miles west of Frederick city. He sent a dispatch to Maj. Gen. Wallace notifying him of his situation. The Union cavalry quickly redeployed where the National Road and Harper’s Ferry Road come together. As Johnson’s advance reached the gap, they saw the valley floor below, and Frederick city in the foreground, as well as troops moving to the scene.
Major General Wallace had ordered reinforcements to the battlefield. The 3rd Potomac Home Brigade, the 159th Ohio mounted infantry, the other gun from Alexander’s Baltimore Battery, and a detachment of the Loudoun Rangers were sent to Clendenin’s position. As the Union reinforcements arrived, Lt. Col. Clendenin handed command over to the senior officer, Colonel Charles Gilpin. Colonel Gilpin established his defensive lines across the National Road. The 3rd Potomac Home Brigade was ordered to a hill, a half of a mile west of Frederick. The three guns of Captain Alexander’s Baltimore Battery deployed at different points in Zimmerman’s field. The 159th Ohio was ordered to support Alexander’s guns, while the 8th Illinois Cavalry held the left flank of the Union line.
Brigadier General Johnson had two tasks ahead of him. The first was to inform Lt. Gen. Early of the enemy in his front, and the second was to determine what they were up against. The only way he would get the answers was to form a plan of attack. Brig. Gen. Johnson knew the city of Frederick and the surrounding area well and this may give him the upper hand.
By 4:00 p.m., the artillery on both sides began to fire, and Confederate skirmishers were sent forward to feel the Federal force in their front. Brig. Gen. Johnson deployed the 8th Virginia Cavalry, and the 36th Virginia Cavalry to the right of the National Road, while the rest of the brigade remained on the road. Brigadier General Johnson studied the situation, and came to the quick realization that he was no longer facing just cavalry, but artillery and infantry as well. The artillery hit the Confederates with great accuracy.
By 5:00 p.m., the 8th Illinois Cavalry dismounted once more for the fight. They were very low on ammunition. An hour later, after keeping the Union front busy, Confederate troopers began shifting their line. Brigadier General Johnson was going to hit the Union left flank, but he needed to shift some of his troops farther to the south in order to do so. As he pressed the Union front even harder, the Confederates took Rizer’s barn, however, they gave it back to the Union forces after some struggle. Soon the Union line began to shift toward its left as support. However, the shooting from the Confederates began to decrease slowly as they ran low on ammunition.
By 8:00 p.m., the engagement had not produced any results, and became a stalemate. As Brig. Gen. Johnson encircled the Union force and prepared to make an attempt to take Frederick, his divisional commander Maj. Gen. Ransom called off the attack. Brigadier General Johnson and Major Gilmor both are furious at their commander’s decision. Maj. Gen. Ransom felt that they were too far ahead of Lt. Gen. Early’s army if support was needed. Brigadier General Johnson was forced to pull his brigade back to the Hagan Tavern, where he made his headquarters for the night.
The next day, the Confederate army would enter the Middletown Valley, by way of South Mountain. Maj. Gen. Wallace took command, and began establishing defenses that stretched six miles along the banks of the Monocacy River. Around midnight on July 9, Major General James Ricketts’ division of the VI Corps began to arrive at Monocacy Junction. They were sent from Petersburg during the Confederate invasion. These men were the only troops that would stand between Lt. Gen. Early’s Confederate army and Washington.