This achievement is pretty easy. It just takes a while to play the 100 games. It doesn't matter if you win or lose.
You can unlock a Tank Destroyer at tier 2 on all of the different nations tech trees except China and Japan. A Tank Destroyer is the symbol with a inverted triangle.
You can check your progress by going onto the stats page while in the garage for each TD you play. Or since you're on the Xbox one version you can check the percentage of the achievement when you press the
button and scroll up to achievements.
This doesn't have to be done all in one TD.