jukka, the diesels that drove a type v11 u-boat were a pair of 6-cylinder 4-cycle engines manufactured to nearly identical designs by MAN and GW. they were extremely lightweight and powerful for thier size. the basic output for these units was 1,160 bhp each. from the b model on, however, the diesels were fitted with compressors which increased the power output of each unit to 1,400 bhp. MAN units were fitted with turbochargers. GW diesels had a geared supercharger driven mechanically by the motors driveshaft. in general the GW design was preferred as being more robust and reliable. there was talk of replacing all MAN engines but in the event this never occured. on the whole,both designs were highly successful, proving to be extraordinarily durable and reliable in operational use. regards, schalke.