The soldiers guarding the entrances to the surrounded Ukrainian military base here just south of the capital, Simferopol, had little in common with their predecessors from past Russian military actions. They were lean, fit and sober. Few if any seemed to be conscripts. Their uniforms were crisp and neat, and their new helmets were bedecked with tinted safety goggles. And there was another indicator of an army undergoing an upgrade: compact encrypted radio units distributed at the small-unit level, including for soldiers standing such routine duty as guard shifts beside machine-gun trucks. The radios are a telltale sign of a...