According to the source, traditional diesel-electric subs like-class ones (Project 636) use batteries supplying the electric motor. If the battery is discharged, submarine must surface and start diesel engines to charge the batteries. That makes subs vulnerable. In hydrogen-fueled engines, electric motors are supplied by hydrogen fuel cells.The new Russian-made engine is an air-independent powerplant. Like other engines of this type, it considerably increases submerged endurance of non-nuclear subs. In addition, it reduces noisiness level. According to the source, Russian non-nuclear submarines powered by air-independent plants would compete with German diesel subs.In July 2012, Russian Navy Commander-in-Chief Admiral Viktor Chirkov decided to resume construction of Project 677 diesel-electric submarines suspended by the ex-commander Vladimir Vysotsky. Earlier, the Navy was not satisfied with characteristics of the new air-independent powerplant for Project 677, it needed improvement.So far, Russia has built only one Project 677 submarine named. She is passing trials at the time. Other two subs of this class,andare being built. Although their construction was suspended, it can be resumed if the hydrogen powerplant is successfully tested, reportsB-90is an experimental submarine, the only one built under Project 20120 in 2008. The sub's hull is a Projectexperimental submarine laid down late in 80's but not completed due to underfinancing.displaces about 4,000 tons. The submarine is used for tests of new weapons and equipment.