A window assembly (10) for use in mass transit vehicles which allows the quick and easy removal and replacement of transparent, sacrificial glazing panels (16) of the window from vandalism and wear. The frame (12) of the window assembly incorporates one or more retainers (31) which fit into slots (30) along the interior sides of the window frame and sandwich the glazing between the frame and the retainers. In turn, the retainers (32) are essentially "locked" into position in the frame by an inner protective panel (16), which significantly inhibits the removal of the retainers from the window assembly when the protective panel is in its desired position against the window panel (14). Once the inner protective panel (16) is removed from the window assembly, however, the retainers and glazing can quickly and easily be removed from the frame, allowing the glazing and any remaining protective panels to be quickly and easily removed from the frame.