UPC-1

The UPC-1 is an automatic level sensor for your model Submarine. When connected into the stern dive plane servo, the UPC-1 will automatically sence any change in the boat's angle and automatically correct the position of the stern planes to counter the angle, keeping the boat level.
The UPC-1 incorporates push button simplicity, shock resistance, fast response and extremely high sensitivity. With a board that's only 1" long and 5/8" wide, we made it small enough to fit into the smallest model submarine 

X-Tail mixer for R/C Submarines.

Small and compact, this unit is only 1/2" x 5/8"