"My first day as a member of the 501st... it was hot, it was sandy, chaotic. Nothing at all like the simulations on Kamino. Of course that's pretty much the way it was for all of us, wasn't it? All that breeding, all those years of training... It doesn't really prepare you for the screaming or the blood, dosen't it? Frankly I'm still amazed we ever made it through the first hour. 

Incredibly, the Five-Oh-First survived the crucible of Geonosis, emerging battle-hardened, and ready for whatever the war would throw at us." 501st journal on the First Battle of Geonosis.

We fight for the Galactic Republic and the Jedi Order. We fight for it's Ideals and Freedoms. We fight to the death to protect the citizens from harm. We attack our people's enemies to bring peace to the Galaxy. We are the Clone Troopers of the Grand Army of the Republic.