DEARDAOIN -- On Dec. 13, 1862, the Irish Brigade of the Army of the Potomac suffered horrendous casualties as they assaulted massed Confederates firing from within a sunken road beneath Marye's Heights during the Battle of Fredericksburg. (Right: Courtesy of Historical Art Prints Don Troiani's "Clear the Way," showing the 28th Massachusetts advancing its colors against Confederate fire at Frederi…