President-elect Donald Trump has nominated as his Army secretary Vincent Viola, an Army veteran who became a billionaire after founding an electronic trading firm and went on to buy the Florida Panthers hockey team. Viola is a 1977 graduate of the U.S. Military Academy at West Point, N.Y., and funded the creation of its highly regarded Combating Terrorism Center after the Sept. 11, 2001, attacks. A former infantry officer and Ranger School graduate, he has pressed for innovation in cyber warfare, saying at a conference five years ago that the Army of the future will be built on a “gestalt...