In order to command a nuke vessel in the US NAvy you must be a nuke officer, SSN/SSBN/CVN etc. It's a pretty intense program, high failure rate etc.me,myself and I wrote:Yes, in the Nuclear Navy, all the officers must have knowledge of how the reactor works/what to do if something goes wrong. And I think (if I recall correctly) you have to have spend some time in engineering before becoming a SSN/SSBN Captain.
That said, a certain amount of cross training is required for a military to function. From the most basic incarnation in the US military to the Commonwealth nations where each soldier has a primary trade and a couple secondary ones. It's a hard issue to balance out and SF doesn't seem to have managed it, Troi not knowing what an atom is anyone?