From: BC, Canada
It's dependent on the ammunition fired by the 125mm gun. A T-80U in 1989 for example would most likely be armed with 3BM-32 rounds, which have certified penetration of 500mm RHA. Since the Soviets prefer VF80 to VF50 however, this figure may be closer to 560mm. There are a number of areas on the M1A1HA that can be penetrated by this round, namely the turret ring, lower glacis, and gun mantle.
Even then, the T-80U can still achieve a soft kill by knocking out the optics, tracks, gun, etc. which have less protection than the frontal armor.
Likewise, the M829A1 equipping high-end US tanks in the late 80's could not defeat the Kontakt-5 armor found on the T-80U and T-72B obr. 1989 (T-72BM ingame), but the optics, tracks, etc. are still exposed on those tanks.
< Message edited by Stimpak -- 11/13/2016 11:59:21 PM >