The 124th broke camp again September 25th, went to Miners' Hill, and here the men became experienced in picket duties. Tents were struck October 16th, and the next day they started in a drizzling rain with their division to join the main army on the Maryland side of the Potomac in the vicinity of Harper's Ferry. A freight train carried them in great discomfort from Washington to Knoxville, eight miles from Harper's Ferry, and they became a part of the Army of the Potomac. October 25th they again received marching orders, and were in motion from supper time till midnight, when they bivouacked near Berlin, where a pontoon bridge was being laid. Across this they went with the entire army of 100,000 men, and were afterward halted in a muddy cornfield near Lovettsville, where they had to stay all night in rain, a cold wind and mud, and had their first realization of the sufferings of army life. The next morning thirty of the men were unfit for duty. Short marches were continued, with stops of two or three days, they being in the advance with the rest of Whipple division a part of the time, and then they looked from a peak of the Blue Ridge upon some white tents of the enemy. The object of the movement had been to cut off a force of his infantry, but it was too late and the division was ordered to retrace its steps. At Orleans they learned that McClellan had been succeeded by Burnside as commander of the Army of the Potomac. November 11th they marched to Waterloo, and here some of the men of Co. B, commanded by Lieutenant W. E. Weygant, were part of a detail which had a fight with the enemy's pickets and captured two prisoners. November 16th they marched to Warrenton and here became a part of General Hooker's grand division. There were now daily marches, some of the time through heavy rains and in deep mud. November 23rd, four miles from Fredericksburg, they went into camp for the first time since leaving Miner's Hill. The army waited in that vicinity for the pontoon trains, which did not arrive until December 10. Then, in pushing a pontoon bridge across the Rappahannock, many of the builders were killed by Mississippi sharpshooters. To stop this 120 cannon were placed on Stafford Heights overlooking Fredericksburg, and began firing shells into the city and among the sharpshooters. When the firing ceased two bridges spanned the river, and Union troops hurried across and soon drove the enemy out of Fredericksburg. But the great battle was yet to come, when the Confederates forced Burnside's army to withdraw to Falmouth after losing 13,000 men. Platt's brigade formed the extreme right of the line, and the 124th was one of the last regiments to recross the bridges. The next morning about half of the men answered to the surgeon's call, and nearly a hundred were placed on the sick list. General Platt resigned about Christmas time, and there was a period of drilling and picket duty by brigades. January 5th the corps was reviewed by General Burnside.