After the formation of the Confederacy and the Battle of Fort Sumter, Congress authorized a massive increase in the number of specialized engineer troops on August 3, 1861, to complement the growing Union Army.

With the volunteer engineers' brigade under BGEN Henry Washington Benham, the 50th moved to Yorktown and worked digging trenches, constructing bridges, and earthworks until the evacuation of that city.

At White House, the command was divided into several detachments, which were engaged in escort duty and bridge building until reunited at Dispatch Station on June 1, when the regiment was employed in providing for the passage of the troops over the Chickahominy.

In response to prodding from Lincoln and general-in-chief MGEN Halleck, Burnside planned a late fall offensive that the relied on quick movement and deception.

On Sunday evening, when he heard Sumner’s men were approaching Falmouth, Lee immediately had Longstreet send two of his divisions toward Fredericksburg.

As these units left their camps the next morning, Monday, November 18, Stuart’s scouts forded the Rappahannock arriving at Warrenton just as the last U.S. troops were departing.

[25] In the meantime, when the AoP started from Warrenton, Sumner's grand division was given the advance; II Corps arrived on Sunday evening, the 17th at Falmouth, opposite the upper edge of Fredericksburg.

[26] When the rest of the AoP arrived two days later, Hooker also suggested crossing, this time at United States Ford, just a few miles upriver.

Burnside, mindful of McClellans problems when a river divided his forces in the Peninsula campaign, again worried that the high water would do the same to him and chose to wait.

[28] Before beginning his campaign, Burnside had arranged for the shipment of the pontoon wagon trains through the Union Army’s General in Chief, Henry Halleck.

[33] Just before he cut his communications with Washington on Sunday, November 17, to make his move, he had tasked his Chief Engineer LT Cyrus B. Comstock to check the status of the pontoons' movement.

But when he saw how slowly Burnside was moving (and Confederate President Jefferson Davis expressed reservations about planning for a battle so close to Richmond), he directed all of his army toward Fredericksburg.

Burnside still had an opportunity, however, because by then he was facing only half of Lee's army, not yet dug in, and if he acted quickly, he might have been able to attack Longstreet and defeat him before Jackson arrived.

On the other side of the Rappahannock, 220 artillery pieces had been located on the ridge known as Stafford Heights to prevent Lee's army from mounting any major counterattacks.

His artillery chief, BGEN Hunt, placed the army’s 312 guns, with 147 of them on the advantageous high ground of Stafford Heights, to support the crossing.

When the bridges were nearly complete, a small Confederate force charged the engineers and inflicted some casualties, but Union artillery fire drove the attackers away.

With so many men, horses, and equipment in motion, secrecy was impossible as each caravan toted 34 pontoon boats on wheels accompanied by 29 support vehicles laden with lumber, tools, and forges.

[43] Brainerd rested in the parlor of the Lacy house, listening to the bell from Saint George's Episcopal Church toll 03:00, and wrote his goodbyes to his family.

[31] On the opposite shore, BGEN William Barksdale alerted his commander, MGEN Lafayette McLaws, that Federal bridge building had commenced.

[49] Brigadier General Henry Hunt, the Army of the Potomac’s Chief of Artillery, had placed his batteries on Stafford Heights, east of the town.

To break the stalemate, General Hunt suggested to Burnside that infantrymen be sent across the river in boats to secure a small bridgehead and rout the sharpshooters.

Burnside suddenly turned reluctant, lamenting to Hall in front of his men that "the effort meant death to most of those who should undertake the voyage."

The Regulars and the 1st New York detachments who had a comparatively easier time saw much less eventful crossings south of the city by Franklin's Left Grand Division.

[52] The clearing of the city buildings by Sumner's infantry and by artillery fire from across the river began the first major urban combat of both the war and American history.

[56][15] After passing the winter in the neighborhood of Fredericksburg, the regiment joined in the Chancellorsville campaign, where it aided effectively in conveying the army across the river and was highly praised by their commander, BGEN Benham.

[69] At the same time, Wright's VI and Burnside's IX Corps would pull out and take separate routes to Jones’ Bridge on the Chickahominy River continuing on to Charles City Court House.

BGEN Ferrero’s division of United States Colored Troops would take a third column with the army’s trains across the Chickahominy east of Jones’ Bridge.

On Thursday, June 9, Meade ordered the construction of a new line of entrenchments in the army's rear, extending northward from Elder Swamp to Allen's Mill Pond.

The engineers would have their work cut out for them as the river was 1,992 feet at that point and the landward approach would needed considerable tree clearage and an extensive trestle ramp.

By Friday morning, June 17, more than 100,000 men, 5,000 wagons and ambulances, 56,000 horses and mules, and 2,800 head of cattle had crossed the river without alerting the Confederates.