I just played a match with my M12 - a tier 7 American artillery.
I killed all 3 enemy artillery, one of which was a tier nine, as well as a tier 7 TD.
I did not get this achievement, nor this one:
The Murica achievement in World of Tanks: Valor worth 86 pointsDestroy 4 enemy tanks in a single match while using an American tank. MP only.
Therefore one or more of the below must be the case:
1. The achievement is buggy (wouldn't be the first time)
2. You cannot get this achievement while playing as artillery.
3. Enemy artillery kills do not count towards either achievement.
Because of that I would recommend playing as a high penetration/damage TD. Hang back and try to steal a kill of a tank that is 2 tiers higher than you.
Since this is a new achievement can people please let me know how you got/get it and I will update this solution