Order 66 never got the chance to be ordered. The Jedi Order Discovered the Sith threat first. Sidious has been defeated, the plans for an empire halted and erased away, Anakin Skywalker has stayed on the Path of a Jedi, and is now a Jedi Knight. General Greivous and Count Dooku are also defeated, along with all other Sith.
But...
The Confederacy was never called off by Sidious. They have grown in strength greatly and now control 2/3rds of the galaxy, pushing the republic in. They have grwon in strength by at least 200 times their orignal military power, and no hope is left for the republic except for the endurance of the Jedi Order and the Clone army. They have attacked the watery world of Kamino first, and caught the clone armies there by surprise. You are an Elite Clone Commando, the most elite ever trained. I will be Jedi Knight Anakin Skywalker, and i will lead you into battle. We have minimal space defenses at the moment. the Confederacy has aquired interdictor technology, and therfore we cannot get any reinforcements unless if we manage to defeat their first wave of ships. The battle will be tough- some of you may fall in the line of duty, but if we work together, maybe we can defeat this enormous threat.
Our current space defenses include a minor netwrok of defense satallites and a deployed minefield, 5 Venator Class Battleships, 8 Acclamator Class Warships, and two legions of assorted fightercraft. Our Ground defenses include 35 million troops.
Once everyone has joined who wants to join, we will begin the battle.

Anakin paced down the aile of Elite Clone Commandos. "Any volunteers?" He asked.

It is your choice whther or not to step forward and ask to be part of the battle now.