Finnish waters are shallow. We could use shallow submarine for military purposes. (or any submarine :-) )
Here we can see a submarine that is 3 meters (118") hight and 8 meters (315") wide. In order to keep it shallow it has telescope sail. The foreplanes are moved to front of the vessel. It was designed based on Swedish Gotland class submarine. This means that it has diesel engines, strirling engines, electric motors and big batteries.
It has torpedos and cruise missiles or mines. The cruise missile launch tubes have an angle that avoid the tailplanes and the propeller.
In this picture we can see the cross-sections of the Gotland-class submarine with hight of 12,5 meters (492") and the Shallow Submarine (the oval one). The volumes of the submarines are: Gotland 1900 m³ (67098 ft³) and the Shallow 1050 m³ (42378 ft³).