Each combatant command (CCMD, also COCOM) is headed by a four-star general or admiral (the CCDR) recommended by the Secretary of Defense, nominated for appointment by the President of the United States, confirmed by the Senate and commissioned, at the President's order, by the Secretary of Defense. The Goldwater–Nichols Act and its subsequent implementation legislation also resulted in specific Joint Professional Military Education (JPME) requirements for officers before they could attain flag or general officer rank thereby preparing them for duty in Joint assignments such as UCC staff or Joint Chiefs of Staff assignments, which are strictly controlled tour length rotations of duty. However, in the decades following enactment of Goldwater–Nichols, these JPME requirements have yet to come to overall fruition. This is particularly true in the case of senior naval officers, where sea duty / shore duty rotations and the culture of the naval service has often discounted PME and JPME as a measure of professional development for success. Although slowly changing, the JPME requirement still continues to be frequently waived in the case of senior admirals nominated for these positions.