Semi-submarine 
Semi-submarines are submersibles that have the capability of diving just like submarines. However they are not able to dive very deep. In fact semi-submersibles immerse so that the vessels' deck is never fully flooded.
The most common design is that of a vessel body just like a ship. The passenger cabin is relatively low, about man's height below sea level. The cabin is equipped with large windows looking out starboard and larboard into the water. The passengers can observe the marine environment that is passed during the voyage.
Semi-Submarines can be used for research, but they are most commonly used in the tourism industry.
