What's the difference between a U-shaped submarine and a modern submarine? Why has the appearance of modern submarines changed? Instead of u-shape

U-submarine belongs to World War II submarine, and its displacement is only 500 tons to 1000 tons. They are all driven by diesel and electricity, and the bomb load is small, so they cannot dive for a long time. Therefore, most of the time they sail on the water. When attacking the target, they also use torpedoes to hurt the target first, and then use deck guns to solve it. Therefore, the submarine shape design at that time was closer to the surface ship, the upper deck was straight, and the water navigation resistance was small.

Modern advanced submarines mostly use nuclear power and AIP power, and can dive continuously for weeks or even months. On the contrary, there are few opportunities for surface navigation, and the displacement reaches thousands or even tens of thousands of tons. In order to reduce the diving resistance, noise and increase the speed, they all adopt a drop-shaped or elongated drop-shaped shape that is more suitable for underwater navigation, and cancel the previous straight deck.