"An intricate dance is taking place in the South China Sea. The dancers are two shoals of fishlike swimming robots; they circle around each other, or drop to the seabed. Some are trying to follow the robots on the other side; some are trying to slip past and remain unobserved. They bunch together, dart in all directions, or attempt to conceal themselves in floating patches of weed. The sea here has a faint noise not heard elsewhere; it closely resembles the usual hum of underwater activity, but it is actually the sound of chaotic acoustic communications. These are underwater modem signals carefully blended to match the background noise, the chatter of the two shoals as they locate, identify, classify, and try to keep tracking the other side. Shipping passes by above, but there are no vessels underwater bigger than a shark. This underwater world of gliding robots, some carrying sensors and some carrying warheads, is not safe for manned submarines. Anything so big and noisy would be instantly spotted and targeted, and as well as their own weaponry both shoals can call on formidable air support. Underwater warfare is now exclusively the domain of robots."

The above excerpt is from the British Study examining the Trident Replacement feasibility and whether the U.K. should spend the money to replace the current Trident fleet. See link.