In Rogue One, as Jyn Erso and Cassian Andor search the Imperial archives on Scarif for the Death Star plans, Jyn rattles off a number of other project names before ultimately finding the one she’s looking for: “Star Dust.”
One of the project names she mentions is “War Mantle,” and we had no clue what that was – until now! In the third episode of The Bad Batch, “Recruitments,” we learned what Project War Mantle was and how it fit into the Empire’s plans.
Almost immediately after the end of the Clone Wars, the newly-formed Empire sent Wilhuff Tarkin to Kamino to discuss the future of the cloning contracts. In a frank conversation with Kaminoan Prime Minister Lama Su, Tarkin insisted that since the cloning contracts were made with the Galactic Republic, the Empire was under no obligation to honor them. Tarkin floated the possibility that enlisted recruits could be just as effective and not nearly as expensive. The Kaminoans strongly disagreed with this assessment, but the Empire continued to test the theory.
With Tarkin still on Kamino, another officer of the Empire, Rampart, who had already been at work implementing chain codes for civilians across the galaxy, brought four recruits to the cloning facilities. These four humans were the first of what Rampart anticipated would be an army of recruits, under the code name Project War Mantle, to phase out the clone army with eager recruits from across the galaxy. Tarkin placed these four recruits under the supervision of an elite clone trooper, Crosshair, whose genetic mutations made him an expert marksman and whose inhibitor chip made him a loyal soldier. Tarkin sent this new squad on a mission to Onderon to eliminate a band of rebels, seeking to test their loyalty to the Empire. One of the recruits defied Crosshair’s orders to commit a war crime and execute refugees, so the clone shot and killed him before ordering the other three to follow his orders. They did so, and Tarkin was pleased with the success of the mission.
As a result, Tarkin promoted Rampart to the rank of Vice Admiral and appointed him in command of Project War Mantle.
So, with all of this information, we now know that this Project War Mantle was the plan by which the Empire began phasing out clone troopers in favor of enlisted recruits, which became known as stormtroopers. This project got underway almost immediately following the conclusion of the Clone Wars, and it obviously was significant enough to warrant inclusion among other top-secret plans like those for the Death Star project.