Short answers, pulled from the story.
The Battle of Fredericksburg took place on the 13th of December 1862. Union engineers began assembling pontoon bridges before dawn on December 11, and the main assault occurred during the day on December 13.
Major General Ambrose Burnside commanded the Union Army at the Battle of Fredericksburg. He assumed command on November 7 after replacing Major General George B. McClellan.
The Union army suffered 12,653 casualties including 1,284 killed, 9,600 wounded, and 1,769 captured or missing. Two Union generals were mortally wounded: Brigadier Generals George D. Bayard and Conrad F. Jackson.
The Slaughter Pen Farm is located about 600 yards west of Fredericksburg near Marye's Heights. It served as the scene of bloody struggle on the 13th of December 1862 where Federal troops under Maj. Gen. George Meade launched their assault against Confederate forces.
The Union attack failed because Confederate artillery provided almost uninterrupted coverage of the plain below while infantry positions behind a 4-foot stone wall proved nearly impregnable. Seven Union divisions sent in fourteen individual charges all failed costing from 6,000 to 8,000 casualties.