The 552nd "Swamp" Legion were perhaps the only Imperial Regiment to declare full allegiance to the Empire Reborn.
Service for the Empire Reborn
Unfortunatley, prior to the attack on the jedi temple, Thunder was sabotaged by rebels and went off route in Hyperspace.
Thunder turned up at yavin a month later and stumbled into the waiting jedi. Only 500 Swamp Troopers survived the massacre. Those 500 fled back to the remnant.
Service for the Second Reborn
When Fleluron seized power, Esha Mayrn saw the same ideals that she admired in him, and promply took her undermanned legion into service with the second reborn.
The 552nd would then lose half teir men in a raid on Yavin under Ven Or.
The legion would set up a stalward defence on Taspir III, and take a heavy toll on the jedi task force, but would be overwhelmed when New Republic reinforcements arrived.
Esha Mayrn followed Fleluron and arrived just after his death at the hands of Luke Skywalker. He would offer her the option of joining the republic, but she pulled out a pistol and attacked luke, condeming herself to death.