US-2 is even more unique than you imagine. A five-engine active lift aircraft. 4 engines for propulsion, 4500 hp each and one active lift boost (also called Border Layer Control), 1300 hp. In the video you can hear the hum of the lift booster engine and you can see the intake/exhaust outlet on the hump at the root of the wing. This fifth engine drives a centrifugal fan (think 1300 hp leaf blower) to supply high-pressure air to the wings as well as the aircraft's tail control surfaces. By blowing air at very high speed through these surfaces, the lift coefficient is doubled - reaching a lift coefficient of US-1, 7. It can produce more than twice the lift per unit wing surface of aircraft of comparable size. Very high lift also keeps the wing small, so its high speed performance is outstanding (i.e. for an amphibian). Thanks to its low minimum flight speed, extremely short take-off and very fast climb, the US-1 can operate in deep troughs of the high seas. As far as I know, this is the only aircraft in the world today that works with such a system.