diesel-electric submarines are quiet making them almost indetectable when using batteries. they are quiter than nuclear subs since they do not need to run pumps during operation. maingay lang sila pag nag-charge ng battery. also meron bago stirling-electric submarine using stirling engines instead of diesels, kahit nagi-snorkel silent pa din. hanapin nyo sa "how stuff works" meron yata article dun about stirling-electric submarines.