TORPEDO ANGLE SOLVER MARK VIII
Torpedo Angle Solver Mark VIII Operating Instructions, O.D. 3518, 1941 describes the hand operated torpedo fire control backup to the automated Torpedo Data Computer. It was commonly called the "banjo" and is used to calculate the angle a torpedo should be fired by an submarine.
INSTRUCTIONS FOR USE
1. The Torpedo Angle Solver Mark VIII is a simple portable instrument designed to compute the required data for firing submarine torpedoes of various marks and powers at gyro angles up to 90 degrees from all classes of submarines.
http://www.hnsa.org/doc/banjo/index.htm