Your new SecDef: What you need to know: The Senate overwhelmingly approved Ash Carter as the new defense secretary Thursday, clearing the way for him to take over the Defense Department's top job.
A trained physicist and a longtime Pentagon bureaucrat, Carter will take office at a time when the military faces political battles at home and complex confrontations abroad.
Carter will be the fourth defense secretary under President Obama, and he'll be responsible for guiding the commander-in-chief's policies through to the end of a tumultuous two-term administration. A rundown on the new boss:
