Realistic difficulty is fairly tough for the inexperienced flight simulator so we'll need to bend the rules a bit. Set your custom difficultly to this:
Thanks to FailedSeppuku for the pictures.
Take off and head for the waypoint.
As soon as you and the other birds are airborne do a big circle to get behind your bombers. This is the opportune position to do the killing of the five (5) enemy planes.
During your flight stick close to the bombers and really focus your attention to the fighters pestering the bombers and not the ones flying around aimlessly.
Speed is of the essence here. And don't worry about black smoke falling planes, the water will kill them for you.