The IKS Ki'tang was a Klingon Bird-of-Prey whose engineer's adjustment to its warp core left it the only allied ship unaffected by the Breen energy-dampening weapon in 2375.
The Ki'tang is a Bird-of-Prey of the Klingon Defence Force that serves in the Dominion War. Its importance is established in the Deep Space Nine episode When It Rains, set shortly after the allied defeat at the second battle of Chin'toka.
In that battle the Breen energy-dampening weapon disabled almost every Federation, Klingon and Romulan ship it struck. The Ki'tang alone kept its power, because its chief engineer had altered the tritium intermix of the warp core to cure an unrelated fault. Once the reason was understood, the same change could be made to other Klingon ships, although it did not work on Federation or Romulan vessels.
For a time this left the Klingon fleet under Martok, and then Gowron, as the only force able to hold the line against the Dominion.