In 2373 Kes, a member of Voyager's crew, found herself some time in Voyager's future. She began periodically jumping backwards in time, despite all efforts to stop her from doing so. In several of the jumps Kes was able to learn considerable detail about what would happen in a possible future for Voyager. The ship went through what the crew called "The Year of Hell", during which time they battled forces of the Krenim Empire. The Krenim used temporal based weapons including chroniton torpedoes. These weapons go into a state of temporal flux when fired, allowing them to penetrate conventional shielding technology with apparent ease. Voyager suffered hits from many of these weapons, taking near catastrophic damage during the year.1
While in this time period, Kes was able to use a tricorder on an unexploded Chroniton torpedo to determine that it had a temporal flux of 1.47. This information was judged to be of critical importance in devising a form of shielding technology which would be effective against these weapons.
With the departure of Kes from Voyager, it seems that the events she experienced were not a part of the preferred timeline.1 In fact when Voyager did encounter the Krenim they proved to be friendly and Voyager avoided their territory due to a dispute which was going on at the time. It is unclear whether the Krenim in the preferred timeline use chroniton torpedoes or other temporal technology.2