Mike,
Been doing some research. I'm sure you are familiar with:
http://www.maritime.org/fleetsub/ele...p3.htm#fig3-05
If you check figure 3-11, you see six wheels at the top of the panel. The center four control the electrical generators, the two outside wheels are for the port and starboard main motors, respectively (the wheels adjust the motor field rheostat, which controls the speed of the motors and thus the shaft RPM. See figures 3-7 and 3-9.
Figure 3-11.
Figure 3-9.
Figure 3-7.