sentences:  Trimming tanks were inside the pressure hull.Ballast tanks were emptied by pressurized air or engines exhaust, thus removing the need for ballast pumps.The boats were powered by two MAN М6V49/48 four-stroke atmospheric reversive diesels (2000 hp each at 465 rev/min) that drove two fixed pitch propellers together with two Electrosila PG-72/35 electric motors (550 hp at 275 rev/min), connecting by BAMAG (Berlin-Anhaltische Maschinenbau AG) type friction clutches.