Yes, the velocity of a fighter plane can affect the overall velocity of a bullet fired from a gun mounted on the plane. When a bullet is fired from a moving platform like a fighter plane, its velocity will be the combination of two velocities: the velocity imparted by the gun itself and the velocity of the plane.
If the fighter plane is moving forward, the velocity of the bullet will be the vector sum of the plane's velocity and the muzzle velocity of the gun. If the plane is moving in the same direction as the bullet, their velocities will add up, resulting in a higher overall velocity for the bullet. Conversely, if the plane is moving in the opposite direction to the bullet, their velocities will subtract, resulting in a lower overall velocity for the bullet.
It's important to note that factors such as air resistance, gravity, and other external forces will also influence the bullet's trajectory and velocity. These factors can complicate the calculations, but in general, the velocity of the fighter plane will contribute to the overall velocity of the bullet when fired from a moving platform.