Hello, Joe

The diesels that drove a Type VII U-boat were a pair of 6-cylinder 4-cycle engines manufactured to nearly identical designs by MAN (Maschinenfabrik Augsburg-Nuremberg) or GX/. They were extremely lightweight and powerful for their size. The basic power output for these units was 1,160bhp each. From the B model on, however, the diesels were fitted with compressors which increased the power output of each unit to 1,400bhp. MAN units were fitted with an exhaust-driven turbo-charging arrangement [Büchigebläse]. GX/ diesels had a geared supercharger driven mechanically by the motor's drive shaft (Kapselgebläse). In general, the GW design was preferred as being more robust and reliable. There was even talk of replacing all MAN engines,' but in the event this never occurred. On the whole, both designs were highly successful, proving to be extraordinarily durable in operational use.
A second set of cams was provided with each engine to allow reversing the direction of rotation of the drive shaft, in order to slow the boat or move it backwards. Switching from normal cams to the reversing cams was a simple operation which required only stopping the engines and throwing a lever at each end of the cylinder bank.

(From "Type VII U-Boats", Robert C. Stern)

Bye
Enrique