A couple days ago we wrote about that badass space-fighter attack boat thing, and we mentioned that it uses "supercavitating technology" to help reduce hull friction. Supercavitation works on bigger boats, too, and a new generation of cargo ships will use lots of little bubbles to improve their fuel efficiency by 25%.
Mitsubishi's Air Lubrication System (MALS) uses an array of powerful air pumps to blow lots and lots of streams of tiny little bubbles through holes in the bottoms of ships. These bubbles create a barrier of air between the hull of the ship and the water, so that much of the ship's hull isn't actually touching the water anymore. This drastically reduces friction, and enables the ship to move either much faster or much more efficiently (pick one). For cargo ships that don't care about moving a lot faster, they can slash their fuel consumption by a quarter, while reducing their CO2 emissions at the same time.
Unsurprisingly, the military has been interested supercavitation for a while now, but for the speed boost as opposed to the efficiency increase. The Russians have a type of torpedo called Shkval that uses supercavitation along with a rocket motor to reportedly reach speeds close to 350 mph while submerged. And, DARPA has reportedly been developing a supercavitating submarine called Underwater Express that can transport troops underwater at up to 115 mph since 2009. So where is it now? Probably anywhere it wants to be.