They eventually began wearing Phase 3 armor, and no longer were they Clone Troopers of the Grand Army of the Republic, but Imperial Stormtroopers of the Galactic Empire. Originally, the Clones wore Phase 2 armor, and still had their original distinguished markings from when they were in their original units during the Clone Wars. ' Darth Vader' (of course) was the leader of the army while Darth Sidious was the Emperor of his very own Galactic Empire. Security, and an entire naval fleet of pilot squadrons. (Later 501st Legion, like with every former squad and battalion.)
Standard 501st Clone Troopers in Phase 2 armor. How the 501st Legion originally was before the development of Phase 3 armor. The 501st consist of having a huge amount of Imperial Stormtroopers (Phase 3 Clone Troopers), small squads of Royal Guards for Darth Sidious ( "The Emperor"), an infantry of Shock Troopers (Sandtroopers) for the Imperial hence becoming the mighty legion led by Sith Lord Darth Vader. during the Clone Wars led by Jedi General Anakin Skywalker, and was formed when the entire Grand Army of the Republic was absorbed into what was left of the 501st Torrent Co. The 501st Legion originally was known as the battalion known as the 501st Torrent Co.
The 501st Legion "Vader's Fist", Imperial Army, the infantry of the Empire or the armed forces of the Galactic Empire, was a legion which was formed during The Fall of the Republic era, when OrderĦ6 the Great Jedi Purge, occured before the Galactic Civil War.