Legion of the 378th

The Legion of the 378th was an Imperial Stormtrooper Legion used first by the Republic for the Battle of Utapau and most of the Order 66 missions. After they found that they had skill in the Rebellion of Tatooine against battle droids, the Emperor decided to use them against any surviving CIS forces, along with their “brother batch”, the Legion of the 614th. Survivors of the battles would declare the fighting as “The Private Clone Wars”.

The Battle of Muunilinst
The 378th was dispatched in their first Imperial mission to take out a group of communication jammers on Muunilinst, as well as some expensive CIS mining equipment. They easily fought their way through orbit and decimated the CIS bases. In addition, the late San Hill's personal fortress was destroyed and the 378th field commander, IG-88, personally slew clones of Count Dooku and Asajj Ventress.

The Battle of Rakata Prime
Next, the 378th was sent to Rakata Prime, where the Force Harvester had been transferred from Raxus Prime and was being rebuilt for uses by the CIS. The 378th, still under the command of IG-88, also destroyed a Jedi Temple and slaughtered survivors of Order 66 and their Wookie protectors, including the Chewbacca's secret half-brother, Verbacca. They then captured maddened Jedi Master Terpes T'mouch, who claimed he had found a holocron with the knowledge of a Force attack called Force Tsunami, and that he would reveal the location if they let him fight for them. Using the Jedi as a weapon, the troops easily overwhelmed the droids surrounding the Force Harvester and destroyed it. The Jedi then told the troops were the holocron was. IG-88 killed T'mouch, collected a bounty, and left.

The Search on Rhen Var
On the outside it seemed that the 378th was simply being sent to destroy a droid facility and capture a Droid Control Program on Rhen Var. However, Darth Vader, their new field commander, was not sent to command but to investigate the mysterious “Forest of Death” that surrounded the city. When he left with a small platoon of troops as the others destroyed the facility, and found that he had to fight off strange entities which simply called themselves “The Guards of the City”. Vader easily killed them and went into the forest, only to be attacked by Force illusions of various creatures that included reeks, acklay, and nexus. He then discovered that the projections were generated by a squad of three Jedi, two of which were human and one was a Gungan. In a small act of mercy, Vader sent the Jedi back to camp with the platoon while he investigated the woods. He found a crashed Wookie starship, which had been shot down by the Force. As Vader studied it, he learned that it was destroyed by a Force Tsunami—the very attack that Terpes T'mouch had locked in his holocron. Vader also learned the ship had incredibly powerful shields, so thus the Tsunami had to be a powerful attack. He returned to the camp to ask the Jedi to teach him the Force attack, only to learn they had killed him men and escaped with the Droid Control Program, hoping to give it to the CIS. Gathering the remnants of the 378th, Vader gave chase after killing the Gungan and one of the humans.

The Hunt on Toydaria
Vader's chase led him to the homeworld of his former slave master, Watto, where he discovered that certain lizards on the planet were jamming him ship and preventing him from using the Force. Therefore, he had to navigate a Force-made maze to reach the base where the Jedi was hiding. He sent his men to kill the lizards so they could leave After doing so and finding the base, Vader killed the Rhen Var survivor while in meditation, only to be attacked by two more. He killed them with ease but found that they had already given the Program to Vilmahr Grahkh, a bounty hunter that was working for former Senator Tikkes and CIS scientist Zian Finnis. Vader entered the hangar right as Grahkh took off and used the magnetic technology in his boots to grab onto Grahkh's ship.

The Mustafar Continuation
In space, Vader broke into Vilmarh's ship and destroyed the autopilot, NT 600. Thus, the ship crashed on Iridonia and Grahkh was killed. Ironically, Iridonia was where Tikkes and Finnis were hiding, so Vader killed them both, along with the battle droid OOM-9, a veteran from Naboo. In the base, Vader also found a clone of Nute Gunray, and he broke open the clone pod. Gunray, still a coward and remembering his death of Mustafar, tried to flee, but Vader broke his arm and left him to die in the desert. He then brought the Droid Control Program to the Emperor.

Bad Blood
Sent back into combat immediately, the 378th was sent to Tipoca City on Kamino, along with none other than Boba Fett, to crush an uprising of clones. It was a fairly simple mission and the entire facility was destroyed. Fett managed to collect a bounty from Ko Sai, Prime Minister Lama Su, and a clone of Tan Wei. During this battle, a Star Destroyed containing a sample of Darth Vader's DNA was destroyed by a Commerce Guild battleship and the samples were stolen, along with the Holocron.

The End of the War
Using the Droid Control Program, the 378th tracked down the CIS Remnants army to Yavin 8, where they created an army composed of the 378th, the 614th, the 783rd, and all the previous field commanders. After destroying the CIS ships so they couldn't escape, the army attacked the base and were met by a number of forces. The 783rd was decimated by the clone of Count Dooku, which now donned a mechanical head to replace the one he lost in combat on Muunilinst. Nute Gunray had copied Vader's brain patterns and could use the Force by making clones of Vader from the samples. Vader easily cut down Dooku and Gunray, but found that Gunray had learned the same Force art Palpatine had from Plageus years before: he could transfer bodies, and had chosen a clone of Anakin Skywalker. The former Viceroy had gone completely mad, and called himself “Anaakin Skywalker”, similar to Luuke Skywalker, a clone of Vader's son who would appear later. Vader found and destroyed the clone bank, and then killed Skywalker. Without their commanders, the droid army was easily and completely annihilated.

The Final Mission
The last known record of the 378th was when they were sent to Byss to crush a human rebellion, the first known record of the Rebel Alliance. Vader and Palpatine then arrived and claimed that the 378th had “seen too much” and killed the entire force personally. It is unknown why they did not kill the 614th.