Surface-underwater ship — an attempt to create a hybrid warship, that combines the properties of a surface ship and submarine. Attempts to create such hybrids were made with the late 19th century to the present time. None of the projects have proved to be successful for a variety of requirements for surface ships and submarines.
The earliest surface-underwater ships considered to be the U.S. Civil War warship USS Monitor.
In the early 20th century was created several ships with a partial immersion of the hull (such as semi-submarine Кета).
Hybridization was in several directions. The first direction — a combination of stealth submarine and firepower surface ship. Examples are the German Type U 139 submarine, British M-class submarine, HMS X1 and French submarine Surcouf. Vertex attempts combination of stealth submarine and firepower surface ship became French submarine Surcouf. The second direction — a combination of stealth submarine and speed surface ship. An example is the British K-class submarine (equipped with steam-turbine units for high speed on the surface) and Soviet submarines type True (with contours destroyer for high speed on the surface).
In the 1960s the Soviet Union developed a draft diving missile boat with hydrofoil for stroke on the surface, capable dive and move underwater. However, the project was closed.
More recently, the French introduced the draft diving frigate SMX-25, capable of diving and moving underwater.
Cocaine smugglers from South America to the United States use Narco submarines.
Surface-underwater ships also use in the navy North Korea and Iran.