Here is the full list of all 24 Gratuitous Tank Battles achievements.
For destroying 2000 enemy infantry
For deploying 3 or more supply trucks in a single engagement
For completing a single battle
For completion of the entire campaign on lowest difficulty
For completion of the entire campaign on middle difficulty
For completion of the entire campaign on highest difficulty
For achieving 100 victories in battle
For fighting 100 battles
For deploying over 1,000 tanks in battle
For deploying over 10,000 men in battle
For deploying over 100 field ambulances
For deploying over 1,000 fixed emplacements
For Demolishing 10 or more emplacements in a single engagement
For deploying over 1,000 mechs in battle
For deploying over 100 command units in battle
For destroying 200 enemy tanks
For destroying 200 enemy mechs
For collecting 20 or more dog tags in a single engagement
For posting 5 or more new or edited maps online
For playing over 20 online games
For fighting over 100 battles as defender
For fighting over 100 battles as attacker
For winning a battle without using infantry
For leading over 200 infantry to escape from battle in a single engagement