Uniworld said the look and feel of the new ships would take inspiration from the rivers they sail on, including the Rhine, Main, Danube and Douro.
Each will feature custom fabrics, hand-carved wood and original artwork, as well as additional suites, dining venues and "ultra-luxurious" amenities.
Ellen Bettridge, Uniworld president and chief executive, said 2027 would be a "milestone" year for the line as it completes its transformation into a "fully Super Ship fleet".
"Our focus has never been on simply adding more ships, but on continually raising the bar on the luxury river cruise experience," said Bettridge.
