Viper 591
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Viper 591 was a Mk. II Viper flown by Louanne "Kat" Katraine. While under the influence of Stims, she crashed it into the flight deck of Galactica while attempting to land (Final Cut).
Note
This may have been meant to be the same craft as Viper 791, which Kat trained in in the episode "Act of Contrition".