The Dark Trooper Phase 1 is a Trooper that is unique to the Galactic Empire, and is available at the Fortress in Tech Level 3. It is an excellent damage-dealer, more effective than the Strike Mech. It can also detect stealth units, like Jedi/Sith with Jedi Mind Trick, or Gungan Frigates.
In Tech Level 4, it can be upgraded to the Dark Trooper Phase 2, which has more hit points and slightly more attack and pierce armor.
"This experimental Tech Level 3 ranged attack unit is more effective than Strike Mechs at dispersing enemy infantry formations, and can detect units that are imperceptible to standard scans — units such as concealed Jedi."