Just finished a biography of Richard Gatling.
If Union supply officers had been a little more imaginative, they could have had 50 or 100 Gatling guns in the line on Cemetery Ridge.
Could have ended the war right there.
A Pair of walkie talkies would have had the same result for the Confederates. Lack of Communication was key to their loss. If Lee had known his cannon shells were mostly falling behind the Union main lines, or if only he knew Jeb Stuart was not going to complete his attack on the other side of Culps Hill, Pickets charge may have never happened and tens of thousands may have lived to fight another battle closer to Washington.