Per the title, Gettysburg is a small town in Pennsylvania where on 1-3 July 1863 a decisive battle occurred during the American Civil War stopping an invasion of the north by Robert E. Lee and the Army of Northern Virigina. At the dedication of the military cemetery President Abraham Lincoln delivered a few remarks now known as "The Gettysburg Address" that is now regarded as one of the most elegant and important speeches in American history.
Alex Diakun reprised his role as Nicholas Prentice from Tribunal (1999) and would later do so again in Time to Time (2001). He is the only actor to play the same character in three episodes of The Outer Limits (1995).
This episode takes place on June 30, 2000, from June 30 to July 3, 1863 and on November 19, 2013.
This is one of only two episodes to feature an historical figure as a character: General Robert E. Lee. The other is Ripper (1999) in which Jack the Ripper and his victims Polly Nichols, Annie Chapman, Elizabeth Stride and Mary Jane Kelly all appear.