UPDATED: This is far easier than I realized. You can use the same tank, on the same map! (Thanks GameGod03!)
You'll get this achievement at the same time:
There are 7 different Proving Grounds game types.
With my re-testing of the maps, I tried out a couple different ones. I believe Standard Battle is fastest!Use Tier 1 tanks
--I used the T1 several times as well as a couple other Tier 1 tanks that didn't work as well. The NC-31 and MS-1 worked well though!
The reason Standard Battle works so well is your teammates are all Tier 2, and all enemies except for one of the last are Tier 1. Your teammates can really help clear the map for you!Each map didn't take me longer than 5 minutes, with the fastest around 3.5 minutes
And a few pointers to watch out for with Standard Battle enemies--they are the same enemies, in the same places every time. I ended up going through the middle of the little village to take out the LTraktor first--he'll shoot at you, but if you park just below the ridge, he'll always hit the ground.
Then I moved up, took out the FT fleeing back to their base on the left side from the 2nd group of enemies spawn.
Next, I would move towards the base--be careful here though! A Medium I and NC-31 spawn and move towards the front of their base and can do a lot of damage. I recommend hiding underneath the cliff near their base ASAP and waiting for your teammates to kill them, or carefully pop out and kill them. Remember, they will always shoot at your center of mass, so you can stick out and shoot them quite safely!
For the last part, the big worry is the far right side. First there will be a LTraktor, followed by a T2 Light. Both of these can do a lot of damage. I recommend helping kill the LTraktor, then running back down the hill in front of the enemy base and let your teammates kill the T2 Light.
That's what worked for me most effectively.
Any suggestions as to what might work better? Let me know!
Old achievement info: