Back in the day (1967-72), RO's were either ET's or IC's (Interior Communications). These ratings had the training in electronic theory necessary for maintenance of reactor instrumentation. On Bainbridge, those who where or would become RO's were in Reactor Controls Division, which was responsible for reactor operation and instrumentation maintenance and repair. ET's first qualified as Reactor Technician, basically on the instrumentation and instrumentation alley watch, the secondary control of the reactor. Once qualified as an RT, you were assigned to instrumentation maintenance and repair. RO was the next, and final qualification for an ET. To get there, you had to qualify on all engine room and control room watch stations. You had to understand all the electrical distribution and plant cross connections. You had to understand the interaction of everything in the plant. Back then, the RO was the second in line watch under the Engineering Watch Officer.
Do I think other ratings could have qualified as a RO, sure, but only if RT was out of the loop.
Oh, when you qualified RO, you also qualified as the senior shutdown watch. I wish they then allowed the Electricians to qualify shutdown, it would have made the in port watch rotation a whole lot nicer.
And another thing. I could draw and talk tech and theory on the valve op system, but man did I have a difficult time looking at the actual maze of piping and making heads and tails out of it.
For the most part, being an RO was boring, the guy who worked his tail off was feed control during rapid maneuvering.