/sci/ - Science & Math

Propulsion is another area of commonality, which comes as a surprise to most. Ion engines are extremely similar in principle to the magnetohydrodynamic drives used experimentally in submarines. Both are essentially electromagnetic linear accelerators, but one uses water as a working fluid rather than ambient ions. Rockets are also employed beneath the sea, in vessels and torpedos which 'supercavitate'; that is, they redirect some of the exhaust out of pores in the nosecone to forcibly create a bubble of gas around the vehicle, so that it bypasses the greater friction of water, which is nearly 800 times denser than air. The Russian Shkval fits this description, as do rounds in some undersea weapons, and most recently Darpa's "Undersea Express" which purports a top speed of 115mph (although the actual top speed is likely to exceed that considerably, as the top speed of SSGNs is reported to be 40mph when crew members candidly admit that it's a deliberately lowballed figure. The true top speed of any military vehicle or weapons delivery platform is always classified).