When World War I started, submarines were considered very insignificant, but by the end of World War II, they had sunk over ten thousand vessels. “ Sinking merchant ships, including [passenger] liners, without warning seemed to be part of the new and terrifying practice of ‘ total war, ’ ” states Norman Friedman in his book Submarine Design and Development.
इससे भी अधिक भयानक वह नाशन था जो दुसरे विश्‍व युद्ध के समय निस्सहाय नागरिकों पर बरसाया था जिन में दो अणु - बम भी शामिल थे ।