What is a defining feature of WIG craft design?

The defining feature of WIG (Wing-In-Ground) craft design is the enhanced uplift from surface proximity. This phenomenon occurs due to the interaction between the aircraft’s wings and the surface of the water or land beneath it. When a WIG craft operates close to a surface, it experiences a significant increase in lift, allowing it to achieve efficient flight with reduced power requirements. This unique design leverages ground effect, making WIG crafts particularly advantageous for over-water travel at low altitudes.

In contrast, the other characteristics listed do not accurately describe WIG craft. For instance, the capability to carry heavy loads underwater pertains more to submarines or other underwater vehicles, rather than WIG crafts, which operate primarily just above the surface. The use of sails for propulsion does not apply to WIG crafts, as they rely on aerodynamic lift rather than wind propulsion. Finally, fixed landing gear pertains to traditional aircraft or ground vehicles rather than WIG crafts, which do not require such features to maintain stability during takeoff and landing due to their operational modality close to the surface.