What is the pay for stg 3 in the navy?

STG3 stands for Sonar Technician (Guns), or a surface ship Sonar Tech, 3rd Class Petty Officer. The military paygrade is E-4.

The ST rating is split into Submarine and Surface specialties, STS (Sonar Technician (Submarines) and STG. This is primarily due to the fact that for surface ASW combat vessels, Sonar is more of an ancillary function (they rely more on ASW aircraft, e.g., helos and P3's) for acoustic information, whereas Submarine Sonar is a primary function 24/7 while the boat is underway.

While the basic sonar training is essentially the same, once you get into advanced maintenance school, it changes considerably, as the STS rating is much more involved and complex.