(covers information from several alternate timelines)
The Krenim warship was a type of warship utilized by the Krenim during the 24th century. These vessels were larger and more powerful than an Intrepid-class starship, due to, in part, their complement of chroniton torpedoes.
In an alternate timeline experienced by Kes while she was living her life in reverse, the USS Voyager encounted a Krenim warship in the first engagement of the "Year of Hell", and suffered significant damage because of its initial inability to compensate for the temporal variance of the Krenim torpedoes. Thanks to Kes' assistance, as a result of her time shifts, Voyager was able to counter the temporal variance and disable the Krenim warship's torpedo launcher. (VOY: "Before and After")
Voyager later encountered a Krenim warship in 2374, after the Krenim weapon ship destroyed the Zahl homeworld. They would continue to be hounded by these vessels throughout the year, to the point of nearly destroying Voyager, before Seven of Nine devised a temporal shield to protect the ship. This class of vessel was erased from the timeline - along with a large area of the Krenim Imperium - following the destruction of the Garenor homeworld by the weapon-ship, and was replaced by the Krenim patrol ship.