PEREVALNOYE, Crimea — 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.

Lean and fit, few if any seemed to be conscripts. Their uniforms were crisp and neat, and their new helmets were bedecked with tinted safety goggles. They were sober.

And there was another indicator of an army undergoing an upgrade: compact encrypted radio units distributed at the small-unit level, including for soldiers on such routine duty as guard shifts beside machine-gun trucks. The radios are a telltale sign of a sweeping modernization effort undertaken five years ago by Vladimir V. Putin that has revitalized Russia’s conventional military abilities, frightening some of its former vassal states in Eastern Europe and forcing NATO to re-evaluate its longstanding view of post-Soviet Russia as a nuclear power with limited ground muscle.

Across Crimea in the past several weeks, a sleek new vanguard of the Russian military has been on display, with forces whose mobility, equipment and behavior were sharply different from those of the Russian forces seen in the brief war in Georgia in 2008 or throughout the North Caucasus over nearly two decades of conflict with Muslim separatists.