So, with the 20th century warships have gotten big. Very big. They are typically too large for rivers. However some rivers are much bigger than others. For instance the St. Lawrence is pretty deep, so a bit of dredging allows large ocean cargo ships to get as far as Montreal. Kolkatta meanwhile also sees some major shipping vessels.
As such, I was wondering what's the farthest inland large modern military vessels could travel (I'm specifically curious about Dreadnaughts, but any modern ships interest me).