Here is the full list of all 40 History Civil War: Secret Missions achievements worth 1,000 gamerscore.
Completed all missions below the target time.
Completed the game on the medium difficulty setting (or higher).
Completed the game on the hardest difficulty setting.
Killed 75 enemies with head shots.
Completed a mission below the target time.
Completed a mission below the target time and completed all the bonus objectives.
Completed a mission with over 95% accuracy.
Killed 750 enemies.
Completed the Siege of Vicksburg mission.
Shot all explosive barrels in every mission.
Killed 50 enemies using sidearms.
Completed The Fall of Vicksburg mission.
Completed the game on the easiest difficulty setting (or higher).
Completed all bonus objectives.
Completed the Captain Blazer`s Scouts mission.
Killed 500 enemies.
Completed the Sabotage at Lynchburg mission.
Completed a mission on land without running.
Earned the rank of General.
Completed the Infiltration of Jackson mission.
Killed 50 enemies using Gatling Guns.
Killed 50 enemies using grenades.
Earned the rank of Colonel.
Completed the USS Pittsburg mission.
Killed 25 enemies using cannons.
Earned the rank of Major.
Completed The Great Train Raid of 1861 mission.
Earned the rank of Captain.
Completed the Sharpshooters at Devil`s Den mission.
Killed 250 enemies.
Completed a mission with over 75% accuracy.
Earned the rank of Sergeant.
Earned the rank of Lieutenant.
Completed The Gray Ghost mission.
Killed 25 enemies using melee attacks.
Earned the rank of Corporal.
Completed Dr.Gatling`s Secret Weapon mission.
Earned the rank of Pioneer.
Completed the Dawn at Chancellorsville mission.
Completed one bonus objective.