In 2256 the USS Discovery destroyed the Klingon flagship over Pahvo, using a long series of spore jumps to break its cloak, and Kol died aboard it.
The Pahvans had sent a signal that drew the Klingon fleet, and Kol arrived in the sarcophagus ship to destroy the planet. Starfleet ordered Discovery to retreat, but Captain Lorca chose to stay and fight, hoping to find a way through the Klingon cloaking device.
Michael Burnham and Ash Tyler beamed aboard the Klingon flagship to plant sensors, while Paul Stamets carried out more than a hundred rapid spore jumps around it so that the ship could gather the data needed to see through the cloak. Burnham confronted Kol and kept him occupied until the sensors finished their work.
With the cloak broken, Discovery destroyed the ship of the dead and rescued Admiral Katrina Cornwell and L'Rell, who had been held aboard. The victory gave the Federation a way to detect cloaked Klingon vessels, but the strain on Stamets made Discovery's next jump go badly wrong.