Here is the full list of all 25 Gulf of Aden - there are Task Force Somalia achievements.
Complete level 2
Complete level 1
Bought and Played the Game
Complete level 3
Complete level 4
Complete level 5
Complete level 6
Complete level 7
Complete level 8
Complete level 9
Complete level 10
Complete level 11
Complete level 12
Complete level 13
Complete level 14
Complete level 15
Complete level 16
Complete level 17
Complete level 18
Complete level 19
Complete level 20
Complete a level using only gunboats
Complete a level using only corvettes
Complete a level using only frigates
Complete a level using only destroyers