Fredricksburg+5

On November 7th, Lincoln replaced General McClellan with General Burnside. Burnside launched a campaign against Richmond. There were 115,000 soldiers in the Federal Army and only a few thousand Confederates. Burnside crossed the Rappahannock River on December 11th and Federal soldiers attacked the Confederates. South of the city, confusion caused the major attack. In the end the Confederates mowed down the Federals. General Burnside made his army cross the Rappahannock once again on December 15. They lost 13,000 soldiers and Burnside was relieved of his command. On the other hand, the Confederates only lost 5,000 men which helped them gain confidence for the invasion of the north the next summer.

Sources: http://www.civilwarhome.com/records.htm