That turbine (turbo booster) keep all DDs crazy behind my XUboat while spiting torps at 25kn at vshort range (<1000m sometimes <500m). Once DD under 200m "crash dive" and turn to one side... the uboat goes deep really quick... and even deeper because its speed.
be careful with that "turbo" switched on, on the way up at max speed (25)... otherwise uboat doesn't stop at periscope depth but flies out of the water (surfaces) :P ... which happened to me a couple times... and was fun to see the results
... try that when closer to BBs and with a fleet of DDs behind to see
Anyway its pure fun doing torpedo runs at 25... silient running is thing of the past
or only valid once the main targets have sunk and DDS fly like crazy dropping DCharges anywhere, everywhere anydepth without luck.