The last of the three Medium tank games played achievements, this is the longest and I would highly recommend trying out as many different medium tanks as you can to get a good taste of variety and see if you want to work through any other tank trees.
This achievement itself is quite easy, just time-consuming. British, Japanese, and US all have a Tier 2 and Tier 3 Medium tank. The other nations are sketchy on medium tanks until higher Tiers. Medium tanks have a diamond with one line through it by their Tier number.
Just start a game with your medium tank, if you get destroyed you can just go straight to your garage and pick another ready medium tank and play another match!