What is this trio of fins at the back of a T-38? On a T-38 Talon on static display at a museum, I spotted a trio of aerodynamically shaped devices located aft of the vertical tail and between the engine aftbodies fore of the nozzles, as shown in the photos.  If these are vortex generators (VGs), what in the world are they doing there where there's no aerodynamic surface aft of them for the energized vortices to flow over? Could they be some other sort of protuberance, such as antennae for some system on the aircraft?
There are a couple of possibilities, both out of the T-38 Flight Operations Manual.

It's a nozzle for a smoke generator.  This was an option on the T-38 airplane to generate a smoke trail behind the aircraft for training purposes.

If possible, inquire if that aircraft was an AT-38B.  Those aircraft apparently had an optional 'ballast box' in that region, which I'm assuming was some sort of a counterweight placed there in conjunction with the bomb racks for practice bombs and other range equipment.

As to the vortex generators?  Who knows!