What side did Chamberlain fight on?

Answer 1

I'm going to have to make the assumption that you're referring to Joshua Lawrence Chamberlain, the only American with the last name Chamberlain famous enough to be recognized by his last name alone.

Joshua Lawrence Chamberlain served in the Union Arm from 1862-1865, entering the army as the Executive Officer of the 20th Maine Infantry Regiment at the rank of Lieutenant Colonel (although originally offered the position of Commanding Officer at the rank of full Colonel, which he refused) he eventually advanced to Division Commander, 1st Division, V Corps at the permanent Army rank of Brigadier General, and the rank of brevet Major General of Volunteers.

Chamberlain's defense of the the Union Army's extreme left on the second day at Gettysburg (a defense for which he was ordered to hold to the last man), which concluded with his ordering a bayonet charge when his men ran out of ammunition, is thought by some historian's to have been the most crucial action of the second day at Gettysburg, saving the entire Union Army from being flanked. For this action, he was awarded the Congressional Medal of Honor.

Chamberlain is equally famous for being the Union officer who formally received the surrender of the Army of Northern Virginia at Appomattox Courthouse. As the Confederate Army paraded in to surrender, he is the officer who ordered "carry arms," saluting the Confederates as they surrendered.