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A Krenim warship fires a chroniton torpedo
Seven of Nine inspects a chroniton torpedo fragment lodged in Voyager's hull
Chroniton torpedoes were ship-mounted weapons utilized by the the Krenim, a Delta Quadrant species which possessed deadly weapons based on temporal science. The torpedoes were capable of passing directly through an enemy's shields due to the fact that they were in a constant state of temporal flux.
In an alternate timeline in 2374, the USS Voyager found themselves under near-constant attack by the territorial Krenim, who utilized chroniton torpedoes to inflict severe damage. Eventually, the crew developed a plan to remodulate their targeting scanners to a parametric frequency, so that they could destroy the Krenim's torpedo launchers before they fired. The plan worked, but not before a chroniton torpedo fragment became lodged in Voyager's hull, leaking chroniton radiation into the ship, necessitating inoculations for the entire crew. Five years later, the dormant chronitons in Kes's cells would be reactivated by exposure to a biotemporal field, causing her to experience a series of backward time jumps. These time jumps were halted in 2373, when The Doctor exposed Kes to a precisely modulated field of antichronitons to purge her system of the radiation. (VOY: "Before and After")
In another alternate timeline, in 2374, Voyager suffered heavy damage from chroniton torpedoes as Voyager passed through Krenim space. Eventually, Seven of Nine and Tuvok developed temporal shields which were effective in protecting Voyager. This timeline was also negated by the destruction of the Krenim weapon ship, which erased its influence from history. (VOY: "Year of Hell")