The Breen energy-dampening weapon could drain a starship's power in an instant and gave the Dominion a crippling advantage after the Breen joined the war in 2375.
When the Breen allied themselves with the Dominion, they brought a weapon that left targeted ships completely without power. Its first major use came at the Second Battle of Chin'toka, where an allied fleet was devastated as ship after ship was disabled and destroyed.
One vessel was unaffected, the Klingon ship commanded by Martok, because of a modification its engineers had made to the ship's power systems. The Klingons applied the fix across their fleet, giving the allies breathing room while the Federation and Romulans worked on a countermeasure.