In November 1862, the United States had a new commander in the East and a simple, sensible plan, and the plan was already dying in a warehouse a hundred miles away.

The commander was Major General Ambrose E. Burnside (North), and he had just inherited the Army of the Potomac (the main Union army in the East) from George B. McClellan (North), relieved in early November for letting Lee’s army escape after Antietam. Burnside did not want the job, and not in the modest way generals usually say so. Lincoln had offered him command of the army twice before, once after the failed drive on Richmond that summer and once after the defeat at Second Bull Run, and both times Burnside had flatly refused it, saying he was not competent to handle so large an army. He took it the third time only because the courier told him that if he said no again, the command would go to Joseph Hooker (North), a rival he could not stand. So the man now leading a hundred thousand men into Virginia had spent months insisting he was the wrong man for it, and now had to do the thing McClellan never would: move fast and hit hard.

So he proposed exactly that. He would march the army southeast to the Rappahannock River, the wide stream that runs northwest to southeast roughly midway between Washington and the Confederate capital at Richmond. He would cross at the town of Fredericksburg before Robert E. Lee, commander of the Army of Northern Virginia (the South’s main army in the East), could figure out where he was going, and then drive on Richmond down the open road south. The whole idea was speed: get over the river and onto the high ground beyond it before the Confederates could gather to stop him.

The plan had one moving part it could not live without. Fredericksburg sits on the far (west) bank, and the Rappahannock there is too deep and too wide to wade. To cross an entire army, better than a hundred thousand men with guns and wagons, Burnside needed pontoon bridges: floating bridges built by anchoring a line of flat-bottomed boats across the river and laying a plank roadway over them. His engineers could throw one across in a few hours, but only once the boats actually arrived. He requested them in early November.

They did not come. Somewhere between Burnside’s order and the riverbank, in the tangle of Army supply bureaus in Washington, the pontoon train was delayed, misrouted, and delayed again. Burnside’s lead troops reached the east bank around November 17 and looked across at a town held by almost nobody. The river was right there. The bridges were not. The first pontoons did not arrive until roughly November 25, more than a week late, and by then the chance was gone.

While the Union army stood on the east bank waiting for boats, Lee used the gift. He marched the whole Army of Northern Virginia to Fredericksburg, dug it into the hills behind the town, and packed the high ground with infantry and artillery. The thing that was supposed to be a race became a siege of a position the enemy got to choose. Burnside still meant to cross and attack. Pride, the country’s hunger for a win, and the lateness of the season all pushed him forward, and none of them was a reason that survived contact with the ground. He would now be crossing a defended river to assault a fortified ridge held by an army that had had weeks to get ready. The battle was half-lost before a shot was fired, by a supply failure in an office.