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During the summer of 1990, we were picking up brand new Heavy Armor M1A1s and turning in nearly brand new one year old regular M1A1s, but I do not know if the new HA tanks we were getting incorporated the changes requested by the Marine Corps. I believe once the changes they wanted hit the production lines, the tank became "common" to both the US Army and USMC.
I don't know when the Marines decided to get M1A1s and when the changes were made to the production lines. Even the new HAs we were getting were made the year before (1989). So HA may have existed prior to Heavy Commons, or they may be virtually the same thing.