The twin vertical tails of the F/A-18 were necessary to offset the vortex flows off the leading-edge extensions of the wings. The twin tails are mounted far forward in order to close the aerodynamic gap between the trailing edge of the wing and the leading edge of the vertical tail. This results in a smooth and drag-free fuselage airflow. In addition to the tails' forward position reducing airflow interference around the engine nozzles, it also saves weight by eliminating the need for any major rear fuselage carry-through structure.
