There are a number of Alien Ranks and they define to some extent the behaviour and capabilities of the aliens in combat. They are also important in terms of research, as some of the knowledge that can be extracted from aliens can only be gained from an appropriately ranked alien.
The ranks that are encountered are:
|Enemy Unknown||Terror From the Deep equivalent|
Note: Despite the names, TFTD Navigators and Squad Leaders are not direct equivalents to the Navigators and Leaders of EU. See the individual rank pages for more details.