Here is the full list of all 7 The Great Emu War achievements.
Get a flock of at least 10 Emus
Get a flock of at least 20 Emus
Kill at least 10 Emus with a Land Mine
Kill at least 10 Emus with one Air Strike
Kill at least 10 Emus with one Trip Wire
Kill at least 100 Emus with the Machine Gun in a single game
Summon at least 3 Paratrooper ammunition in 1 game