Dagobert Müller and the Versuchsgleitboot
Müller developed the concept of a hovercraft, which he called a Versuchsgleitboot (roughly translated as gliding boat), in 1915. He submitted a paper outlining the concept to his naval commander. This paper described his experimentation with hovercraft models, through which he developed a concept for a boat using four aircraft engines in total. Three large engines, of 120 horsepower, would be used to provide propulsion, while the fourth, a 65 hp. model, provided lift. The lift-producing engine was to run an air compressor with a theoretical flow rate of 450 m3/min of air.
Müller's designs suggested a top speed of 32 knots, which was quite fast for ships of the day. The ship would have a displacement of 12.05 tons (12.25 tonnes) and dimensions of 16.3 x 6.6 x .75 meters, taking a rectangular shape. Unlike modern hovercraft, the Versuchsgleitboot had skirts only at the sides, not at front or back. The engine creating the air cushion was located towards the front of the boat and was capable of lifting the boat up to 10 inches off the water's surface.
Interested by Müller's work, Austro-Hungarian naval commanders approved the construction of a prototype. They made some significant changes, however. The prototype was lighter, with a displacement of just 7.6 tons, and had more powerful engines. In addition, only the rear section of the hull was to hover; the front would still float on the water. A step was employed to delineate the floating and hovering segments of the hull. A specially-shaped air duct was placed right at this step to prevent unstable flow patterns from developing. The duct was shaped in the form of a swallowtail.
The prototype was completed and underwent substantial testing. These tests revealed a speed boost of 2-4 knots, depending on speed. However, due to the hull's design, the craft came completely out of the water at speeds higher than 20 knots.
Ultimately, the military review board found several problems with the Versuchsgleitboot. The craft was unstable, particularly in high seas. It was also not particularly good at launching torpedoes or depth charges, which limited its effectiveness as a military craft. For these reasons, the board did not recommend further development, and the craft was abandoned for some time.
A Finnish engineer, Toivo J. Kaario, developed another boat that some consider the first "true" hovercraft in 1931. It used similar principles as the Versuchsgleitboot, with only minor changes, so it seems more reasonable to credit Dagobert Müller with the first hovercraft. Interestingly, a Soviet engineer came back to Müller's work in the years before WWII, and was able to achieve speeds of up to 70 knots. He, too, had to abandon his work due to practicality concerns, and the first modern hovercraft was only developed in the 1950's (by Christopher Cockerell).