The four S-Boats of the Schnellboot 1931 class were the first small class of S-boats build by the German navy after World War I. Roughly based on the prototype boat S1 , they were mainly used as testbeds to further develop this kind of boats.

Unlike the later boats, they had the more dangerous fuel engines instead of diesel ones, since the engine suppliers were not able to deliver powerful enough diesel engines.

The four boats formed a so called "Half Flotilla"  and together they trained S-boats tactics for later use.

None of the boats was used during World War II, they all were sold to Spain in 1936.