GLW<------ enlisted as a non-nuke with an eye towards nuke,....
You enlist into a specific group driven by your ASVAB, the current needs of the Navy as manifested by the recruiters "push", and the candidates personal "dreams",...
A construction or aviation group sailor will not likely become a nuke because he/she will not be eligible to strike for a nuke rate,...
To move over to fireman or seaman after enlisting as construction or aviation would require intervention by a nuke recruiter at a training command and that would require the NNPP hopeful to be cognizant of that option and moxie enough to pursue it as there will be little to no encouragement within that recruit's (or apprentices') community or chain of command,...
IIRC there may have been an open call for nuke wannabes to make the attempt during boot camp once upon a time which may still occur in today's USN, somebody with a contemporary finger on the pulse of NTC will have to vouch for that,...
I do not remember any other after enlistment crossover candidates while I was in the USN but I have met and worked with two of them since I went civilian,...
They were both superlative masters of their craft, they were also both former ELT's, superlative becomes a bit redundant when referencing an ELT and therefore may not be representative of other "typical" NNPP candidates from communities other than initial enlistment types,...