Socialist Federal Republic of Yugoslavia
Regarding rivers, the Danube was navigable throughout its entire course in Yugoslavia, linking the ports of Belgrade, Novi Sad, and Vukovar with Central Europe and the Black sea. Long stretches of rivers Sava, Drava and Tisza were also navigable.
Nazi rule over the Danube River
It is clear that Great Britain, being removed thousands of kilometers from the Danube, cannot be classed as such a State.