The incomplete battleships are more open ended options, but other ships can feature nuclear propulsion too. There were proposals for equipping ships with nuclear propulsion pods that they could use for cruise operations in order to save fuel. The Soviet/Russian
Kirov class battlecruisers actually use a similar hybrid approach, although I'm pretty sure the reactors are inside the hull.
I'll have to crunch the numbers to see what a pod capable of sustaining a 20 knot cruise would look like.
I also need to think of what would happen if the pod were to be lost. They could fall off due to a collision or someone might try to sever one while the ship is stopped in port. They might have to use fuel enriched below 20% to reduce the risks associated with a lost pod. Also, 20% and lower fuel enrichment would be commercial grade, so the equipment could be used for other applications.