A Krenim torpedo that exists in a state of temporal flux, allowing it to pass straight through conventional shields, and the weapon that wore Voyager down during the Year of Hell.
Chroniton torpedoes are the standard armament of Krenim warships. Because each one is slightly out of phase with normal time, ordinary deflector shields cannot stop it, and even small Krenim patrol ships can inflict heavy damage on a far larger vessel.
The weapon is first described in Before and After, in which Kes relives a future where an unexploded torpedo lodged in a Jefferies tube poisons her with chroniton radiation. She brings back its exact temporal variance as a warning.
In Year of Hell, the attacks happen. Seven of Nine and Tuvok examine a dud torpedo to obtain the variance, which lets the crew build temporal shielding, but the device detonates and costs Tuvok his sight.