The Spy War: How the C.I.A. Secretly Helps Ukraine Fight Putin

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 drone threading through Russian air defenses from a point in central Ukraine to a target in the Russian city of Rostov.

The underground bunker, built to replace the destroyed command center in the months after Russia’s invasion, is a secret nerve center of Ukraine’s military.

There is also one more secret: The base is almost fully financed, and partly equipped, by the C.I.A.

“One hundred and ten percent,” Gen. Serhii Dvoretskiy, a top intelligence commander, said in an interview at the base.

Now entering the third year of a war that has claimed hundreds of thousands of lives, the intelligence partnership between Washington and Kyiv is a linchpin of Ukraine’s ability to defend itself. The C.I.A. and other American intelligence agencies provide intelligence for targeted missile strikes, track Russian troop movements and help support spy networks.