WASHINGTON (AP) — Defense Secretary Lloyd Austin is vowing he “won’t let grass grow under our feet” as the department begins to implement new vaccine and testing directives.

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But Pentagon officials are scrambling to figure out how to implement the changes across the vast military population and determining which National Guard and Reserve troops would be affected by the orders.

The Pentagon has two missions: It must develop plans to make the vaccine mandatory for the military, and also has to implement new requirements for federal workers who will have to either attest to a COVID-19 vaccination or face frequent testing and travel restrictions.