Here is the full list of all 15 Six Days in Fallujah achievements.
Complete a mission during a Sandstorm.
Congratulations! You earned your first stripe!
Complete a mission during the "Flare" Time of Day.
Complete a fireteam mission playing the FIRE role, who uses the M249 SAW and specializes in suppression
Complete a fireteam mission playing the ASSIST role, who specializes in CQB
Complete a fireteam mission with a full fireteam of players from your Friends List.
Complete a fireteam mission playing the READY role, who specializes as the fireteam's scout
Interact with a downed teammate to prevent bleeding out and bring them back into the battle.
Play Six Days for six hours.
Successfully complete a 4 player fireteam mission as Team Lead with minimal loss
Complete a FUBAR Apartment Building Mission with Hard AI difficulty.
Complete a FUBAR Jolan Public Park Mission with Hard AI difficulty.
Complete a FUBAR Phase Line Henry Mission with Hard AI difficulty.
Complete a FUBAR mission on Hard AI difficulty, with no deaths.
Complete a FUBAR Northern Train Station Mission with Hard AI difficulty.