A general or flag officer, probably from the Marines.
My best guess.
5.56mm
“Command” of NSA rotates between the Army, Navy and Air Force. Alexander is an Army four-star; his predecessor, General Mike Hayden, was an Air Force general; unless Barry decides to break the rotation, the next NSA Director will be a Navy Admiral.
Both Alexander and Hayden are the longest-serving NSA directors in history; between them, they held the job almost 14 years. DIRNSA was formerly a three-star billet; it was elevated to four-star rank after 9/11. The last NSA director who served a “normal” three-year tour (as a Lt Gen or Vice Admiral) was Lt Gen Ken Minihan, who retired in 1999.
NSA’s growth over the past two decades, both in size and power, has been jaw-dropping. And virtually no one shows any inclination to reign in the agency, and its reach. Go figure.