On the 7th, Confederate General Imboden stopped Buford's Union cavalry from occupying Williamsport and destroying Confederate trains. Federal General Kilpatrick's cavalry division drove 2 Confederate cavalry brigades through Hagerstown before being forced to retire by the arrival of the rest of Stuart's command. Lee's infantry reached the rain-swollen Potomac River but could not cross, the pontoon bridge having been destroyed by a cavalry raid.

French got to Williamsport before the Confederates and destroyed the pontoon bridges as ordered. Knowing that it would take at least 6 days to get everybody across, including equipment, Lee decided to make a stand against the Union army before he proceeded with his retreat. Lee's defenses were from Downsville around to Falling Waters on Concoteague Creek, both ends of the 5 mile line secured by water.

After successful in the United Kingdom, railway post offices in the United States were introduced on July 7, 1862 using converted baggage cars on the Hannibal and St. Joseph Railroad (which also delivered the first letter to the Pony Express). Purpose built Railway Post Office cars entered service on this line a few weeks after the service was initiated. Its purpose was to separate mail for connection with a westbound stage departing soon after the train's arrival at St. Joseph. This service lasted approximately one year. The first permanent Railway Post Office route was established on August 28, 1864 between Chicago, Illinois, and Clinton, Iowa.

There is to be a convoy of gunboats each day from Harrison's Bar to near the mouth of the Chickahominy, going and returning each day. As there was no better reason for the time than the arrival and departure of the mail from Old Point, it was agreed that at 9 a.m. all the transportation down should sail, convoyed by gunboats-I had selected four for it. And at 3 p.m. all the army transportation to this point should come up, convoyed by the same force." Convoy and cover of supply ships by the gunboats were indispensable to General McClellan's army.

During the summer of 1862, Federal Maj. Gen. Samuel R. Curtis planned to move his army toward Helena in search of supplies to replace those that had been promised but never delivered by the Union Navy. The Confederates under Maj. Gen. Albert Rust attempted to prevent this change of supply base by continually skirmishing with the Union troops. They skirmished with Union troops as the Federals marched south along the White River toward the supply flotilla waiting at Clarendon.

On July 7, Confederate Maj. Gen. Thomas C. Hindman ordered Brig. Gen. Albert Rust to stop them at the Cache River. Rust moved too slowly, so the forward elements of his force did not strike until 4 miles south of the river on Parley Hill's plantation near Cotton Plant. The outnumbered Union forces, commanded by Col. Charles E. Hovey, repulsed repeated, poorly organized attacks by Col. William H. Parsons' 2 Texas cavalry regiments. The fighting became more general, and the Confederates, with a frontal attack, forced the Union to retreat about a 1/4 mile. The Confederates fled when Union reinforcements arrived.

On July 8, the 2nd Wisconsin Cavalry, under the command of newly promoted Brig. Gen. Cadwallader C. Washburn, pursued the Confederates to the Cache River, destroying 2 ferry boats and capturing several prisoners. With reinforcements, the Federals pursued the retreating Confederates and turned the retreat into a rout as the day progressed. Curtis was able change his supply base. But Rust, despite suffering a defeat at Hill's Plantation, remained between Curtis and Little Rock, his objective.

Curtis proceeded to Clarendon only to find that the flotilla had departed the previous day. He turned east toward Helena and occupied it on July 12. Union forces controlled the town for the duration of the war.

The Battle of Cotton Plant was significant because it had an observable influence on the outcome of the Vicksburg Campaign. The victory enabled Union forces to move toward Helena and occupy that strategic town on the Mississippi River for the duration of the Civil War. The Battle of Cotton Plant was also known as the Battle of Hill's Plantation or the Battle of Cache River.

During the course of the war a variety of ingenious torpedoes destroyed or damaged some 40 Union ships, forecasting the vast growth to come in this aspect of underwater naval warfare.