The Historical Battle Add-on for Halo Wars has 4 achievements worth 100 gamerscore.
Hot drop 50 squads to your Covenant Leader in a single game on Barrens.
Finish with 5000 net resources tributed to your teammates on Memorial Basin except in Deathmatch.
Kill 20 enemy squads with a continuous Covenant Leader Power on Memorial Basin.
Disrupt 5 active Leader Powers in a single game on Blood River.