In mid-December, after weeks of impatiently waiting both for their supplies to arrive, Union engineers finally had what they needed to begin work on the pontoon bridges necessary to cross the icy, swollen Rappahannock River. Waiting diligently on the river's opposite side, Confederate Brigadier General William Barksdale's Mississippians sniped at the men in blue from the cover of the buildings and other structures in town. Despite their efforts, the engineers soon discovered that they could not finish the pontoon bridges under such a constant deadly fire. After a fierce shelling of the town failed to dislodge their southern foes, Union soldiers climbed into several of the pontoons and braved the hail of lead, rowing across the river to drive their antagonists from the area. After the successful crossing and a bloody street battle, Barksdale's Mississippians eventually withdrew. Their tenacity however gave Robert E. Lee's men the time they needed to strengthen their already strong positions making their works beyond the town nearly impregnable.

Colonel Norman J. Hall, commander of the brigade to which the 7th Michigan belonged, wrote this of the 7th's actions in crossing the treacherous river. "On the evening of the 10th instant, my command was designated to take the advance of the army, as soon as the bridges should be built, on the following morning. On arriving at the point where the head of the column was to rest, I received orders to report with the brigade to Brigadier-General Woodbury, commanding Engineer Brigade, at the Lacy house. The bridges were not being advanced on account of the deadly fire of the enemy's sharpshooters, posted behind buildings and in cellars and rifle-pits along the opposite bank. Two regiments were deployed (the Seventh Michigan and Nineteenth Massachusetts Volunteers) along the bank of the river to cover the bridge-builders by their fire as skirmishers, but afterward withdrew them, to enable the batteries to fire shell. After some hours of delay, Generals Hunt and Woodbury consulted with me upon the practicability of crossing troops in boats, and storming the strong points occupied by the enemy, so as to protect the heads of the pontoon bridges, of which but one had progressed to any extent. It was arranged that, under cover of a heavy artillery fire, the engineers should place boats at intervals along the bank, and provide men to row and steer them.

Lieutenant-Colonel Baxter, commanding Seventh Michigan Volunteers, was informed of the plan, and his regiment volunteered to be crossed and storm the town as proposed. Captain Weymouth, of the Nineteenth Massachusetts, also volunteered to support the Seventh Michigan, if required, crossing in the same way.

The first-named regiment was deployed, and took post along the bank, while the latter lined the river as sharpshooters, together with Captain Plumer's company of sharpshooters (independent), which was ordered to report to me for this object. At a signal, the batteries opened their fire, and continued with great rapidity for over half an hour, the engineer troops failing to perform their part, running away from the boats at the first fire from the enemy and seeking shelter.

No prospect appearing of better conduct, I stated to Colonel Baxter that I saw no hopes of effecting the crossing, unless he could man the oars, place the boats, and push across unassisted. I confess I felt apprehensions of disaster in this attempt, as, without experience in the management of boats, the shore might not be reached promptly, if at all, and the party lost. Colonel Baxter promptly accepted the new conditions, and proceeded immediately to arrange the boats, some of which had to be carried to the water. Lieut. C. B. Comstock, chief engineer, Army of the Potomac, directed the embarkation personally, I believe. Before the number of boats fixed upon had been loaded, the signal to cease the artillery firing was made, and I thought best to push those now ready across, rather than to wait till all were filled, and to allow the enemy to come out of his concealment from the cannonade.

The boats pushed gallantly across under a sharp fire. While in the boats, 1 man was killed and Lieutenant. Colonel Baxter and several men were wounded. The party, which numbered from 60 to 70 men, formed under the bank and rushed upon the first street, attacked the enemy, and, in the space of a few minutes, 31 prisoners were captured and a secure lodgment effected." [5]

Union soldiers moved across the Rappahannock River at three separate locations prior to the battle. They did so at the above mentioned upper crossing, and also at the southern end the city at a section now commonly called "The Middle Crossing" with the third and lower crossing completed further down the river nearer to Confederate Lieutenant General Stonewall Jackson's lines. Union Major General William B. Franklin's Grand Division ventured over the pontoons at the lower crossing, a force which included the men who would later assault Jackson's lines during the earlier stages of the battle. Major General Joseph Hooker's Grand Division, with the exception of some detachments, forded the river at the Middle Crossing pictured on the left.

According to Major General Lafayette McLaws, General Barksdale's small force had a proportionately grand impact on the ability of the Confederate to later fend off their Union attackers. "General Franklin's command had constructed a bridge or two across the Rappahannock, below the mouth of Deep Run, and had crossed the greater portion of his division on the 11th, yet, because of the failure of General Sumner's grand division to force a crossing in front of Fredericksburg, all but one brigade of Franklin's grand division had been recrossed to the left bank to await the result of Sumner's efforts, and that Franklin's grand division was not again crossed to our side until the 12th. The Federal accounts show that this determined defense offered by a small fraction of Barksdale's brigade not only prevented Sumner's crossing, but by this delay caused the whole of Franklin's Left Grand Division, except one brigade, to recross the Rappahannock, and thus gave General Lee twenty-four hours' time to prepare for the assault, with full notice of the points of attack." [59]