http://208.84.116.223/forums/index.php?showtopic=26751
http://www.militaryphotos.net/forums/showthread.php?190335-M1A1-Abrams-tanks-arrive-at-Camp-Leatherneck&s=52dc1351c41828a7f44c75fe653521b2
From what I gather, both variants use an A2 turret. The difference is that the jarhead version (HC) has an electro-optical jammer installed in the, for lack of better term, hole where the CITV would be mounted on the turret roofs of the Army HAs. The A1 HA has a cover plate bolted over that hole.