Often referred to as Gettysburg-64, this replaced the short-lived 1961 hex-grid version in the Avalon Hill wargame line.
The board is a 19th century-style topographic map of the battlefield area, with an overlaid grid of 1-in squares, essentially identical to the 1958 version map. Scale: 1-in to 1/4 mile. Turns are 1 hour; units represent infantry divisions, cav brigades and independent artillery battalions (CSA) or brigades (USA) (Artillery attached to US Corps or CS Divisions is subsumed into the parent units, apparently).
Counters are die-cut 1/2x1/2-in squares for HQ, 1 x 1/2 in rectangles for Infantry, 3/4 x 1/2 for Artillery and 7/8 x 1/2 for Cav (most are a little smaller than their 1958 version equivalent). Units have facing and exert zone of control to the front. Movement, unlike the '58 version, but like all other AH wargames of its period, is rigidly regulated by the map grid. Gone are the outposts and hidden movement that gave the earlier version some of its uniqueness in this era.
This 1964 version was eventually superseded in the AH line by the 1977 version, a major rewrite and a reversion to the use of a hex grid map.