Viper 8757NC is the designation of two Vipers, one Mark II and one Mark VII, assigned to Galactica'.
The Viper Mark VII version appears in "Lay Down Your Burdens, Part I".
A Viper Mark II of the same designation is flown by Kara Thrace during a Combat Air Patrol protecting a Fleet underway replenishment operation. This Viper is the one Thrace is later lost in, crushed by intense atmospheric pressure (Maelstrom). Over two months later, Thrace returns under mysterious circumstances is a remarkably pristine version of this Viper. She claims to have been to Earth and that only a few hours passed for her, but has no recollection of how she got there or how she survived ("Crossroads, Part II", "He That Believeth In Me").