The former Deputy Chief of Naval Operations, Vice Admiral Danforth Whitcomb, was given tactical command of the Reach Theatre of Operations after Reach HighCom was overrun by covenant forces. He and a number of Spartan-II personnel were rescued by the survivors of the Halo conflict, and he eventually met his death crashing a captured Covenant ship into an enemy space installation. It is unknown whether a new Deputy Chief of Naval Operations has been appointed.
In the modern US Navy, the position is also called the Chief of Naval Personnel. The DCNO performs all strategy and resource policies and serves as a single resource sponsor for all manpower and training program matters. The DCNO also performs all Capitol Hill related duties, including all Congressional testimony for matters pertaining to the Manpower, Personnel, Training, & Education command. The DNCO's office also acts as the lead organization to interface with Department of Defense (DOD) and Department of the Navy (DON) officials, other U.S. military and foreign departments, other Navy commands, other Federal agencies, and private organizations. It is unknown exactly how this fits into the UNSC's political structure, though its purpose is presumed to be the same.