In the darkness of the cellar in the eastern Ukrainian town of Toretsk, the soldiers did not know how close the Russian glide bombs were landing. But the sudden change in air pressure that accompanied bone-rattling booms testified to the bombs’ destructive force as they tore into nearby buildings.

At dawn, during a lull in the attacks, several Ukrainian soldiers dashed out and saw a fire triggered by one of the bombs still raging through the ruins of a building about 150 yards away — the narrow margin between life and death.

There are many ways to kill and be killed in Russia’s war with Ukraine, but Ukrainian soldiers say that glide bombs are perhaps the most terrifying. They are free-fall bombs, many left over from the Soviet era, but now outfitted with pop-out wings that feature satellite navigation, turning them into guided munitions.

Referred to alternatively as “KABs” or “FABs,” they weigh between 500 and 6,000 pounds and are packed with hundreds of pounds explosives. A single blast can reduce a high-rise apartment building to rubble and obliterate even concrete fortifications.

“It is scary and very fast,” said Stanislav, a 28 year-old Junior Sergeant with Ukraine’s 32nd Mechanized Brigade, as Russian fighter jets unleashed the powerful guided bombs in the direction of his unit. “I just pray every time.”

In recent months, Russia has used the bombs to devastating effect, tilting the balance of fighting in eastern Ukraine in Moscow’s favor and allowing Russia to continue to make steady gains in Donetsk region. The bombs have also allowed Russian forces to raze whole towns and villages with ever greater speed.