In early November, Maj. Gen. Ambrose E. Burnside took command of the Army of the Potomac, and made immediate plans to move the army once again toward Richmond. He hoped to move quickly, and cross to the south side of the Rappahannock River before Robert E. Lee's Army of Northern Virginia could block his route. On November 14th, Burnside sent a corps to occupy the vicinity of Falmouth on the river opposite Fredericksburg. The rest of the army soon followed. Lee reacted by entrenching his army on the heights behind Fredericksburg. Burnside's army was delayed on the north bank because he had not yet received the necessary pontoon bridges he needed to cross the river. After two weeks, the overdue bridge materials finally arrived. On December 11th, Union engineers laid six bridges across the Rappahannock under fire, shelling the town in the process to drive out Confederate skirmishers. On the 12th, the remainder of the Federal army crossed over, and on December 13th, Burnside mounted a series of futile frontal assaults on Prospect Hill and Marye’s Heights that resulted in staggering casualties. Maj. Gen. George G. Meade’s division, on the Union left, briefly penetrated Gen. "Stonewall" Jackson’s line but was driven back by a counterattack. Union Generals C. Feger Jackson and George Bayard, and Confederate Generals Thomas R.R. Cobb and Maxey Gregg were killed. On December 15th, Burnside called off the offensive and recrossed the river, ending the campaign. He would be relieved of command before the end of January.