For more than a decade, the United States has nurtured a secret intelligence partnership with Ukraine that is now critical for both countries in countering Russia... Nestled in a dense forest, the Ukrainian military base appears abandoned and destroyed, its command center a burned-out husk, a casualty of a Russian missile barrage early in the war. But that is above ground. Not far away, a discreet passageway descends to a subterranean bunker where teams of Ukrainian soldiers track Russian spy satellites and eavesdrop on conversations between Russian commanders. On one screen, a red line followed the route of an explosive...