>>63955414
>>63955478
Atom would easily power a giant forever flying VTOL aircraft (there was a prototype that flew a nuclear reactor)
The first problem is converting the 100% thermal energy into electrical/mechanical energy so it does propulsion.
The second problem after that is shielding and maintenance.
On a boat/submarine you can easily afford the mass of shielding and spread apart components to lessen radiation difficulty.

And obviously there's a 3rd problem of whether it is worth risking a nuclear reactor falling from the sky.