To unlock this achievement you need to play through all 14 missions in the game. This can be done on any difficulty level so to make it quick I would recommend playing through on Easy if this is your first go.
The 14 missions are as follows:
Mission 1: Saint Lo – American Mission
Mission 2: The Island – American Mission
Mission 3: Night Drop – British Mission
Mission 4: Mayenne Bridge – American Mission
Mission 5: Falaise Road – Canadian Mission
Mission 6: Fuel Plant – British Mission
Mission 7: The Black Baron – Polish Mission
Mission 8: The Forest – American Mission
Mission 9: Laison River – Canadian Mission
Mission 10: The Crossroads – American Mission
Mission 11: Hostage – British Mission
Mission 12: The Corridor of Death – Canadian Mission
Mission 13: The Mace – Polish Mission
Mission 14: Chambois – American Mission