Here is the full list of all 40 Defend The Highlands achievements.
Kill 1,000 enemies with turnip turrets
Kill 1,000 enemies with haggis catapults
Kill 1,000 enemies with porridge cannons
Kill 1,000 enemies with golf balls
Kill 250 enemies with bagpipe artillery
Kill 10,000 enemies
Get 500 kills with Queen Boadicea
Kill 500 enemies with cheese wheels
Kill 500 enemies with whisky vomit
Recruit 1,000 Scotsmen in total
Kill 500 enemies in melee
Get 500 kills with William Wallace
Kill 500 Beefeaters
Complete a skirmish match on impossible
Kill 500 Leprechauns
Hit 5 enemies with a single artillery strike or haggis
Complete a skirmish match on hard
Defeat a level 6 enemy on level 1 in skirmish mode
Complete a skirmish match on medium
Complete a skirmish match without heroes
Complete a skirmish match without towers
Kill 500 Welsh Sheep Riders
Complete a skirmish match on easy
Kill 500 Posh Englishmen
Kill 500 Ancient Briton Warriors
Get 500 kills with Robin Hood
Kill 1,000 enemies with porridge bowls
Have 5,000 porridge at once
Fully upgrade all stats on a single unit
Have 50 Scotsmen at once
Kill 500 English Cricket Players
Kill 500 Irish Potato Farmers
Fully upgrade a stat
Kill 500 Welsh Rugby Players
Recruit 100 Scotsmen in total
Have 2,000 gold at once
Kill 1,000 enemies
Get 500 kills with Alfredo
Kill 15 enemies with Nessy in a single match
Kill 100 enemies