Click on the sonar to bring up the "toolbar" options first icon on the left should be "go to sonar station"
If you find yourself in the conning tower just click on the sonar station. Oh and watch out for the red buttons behind you, they will fire your torps.
You can also use your mouse pointer to direct the dial by clicking on the dial face, hope that makes sense.
Don't try to find the guy at 180 degrees otherwise your going to be chasing your tail
Good Luck