That isn't true either. I was the first (and probably only) MM to qualify Throttleman in the 704 boat.
All of the MM's were qualified Throttleman on the 724. In either case, only ET's and EM's stood the watch on the regular rotation. ET's and EM's are not trained to maintain the Main Engines, Reduction Gears, or the Hydraulic Throttle Control System.
I'm still waiting for someone to tell us about the days when Enginemen were qualified RO and IC's were the other source rating for ELT. Maybe they are all long gone by now.
While things may have changed since 1967-1970, with the exception of the engineering watch officer, RO's had to qualify on every watch station in the engine room, including ELT as it related to the reactor coolant and SG's. The qualification process included the understanding of the inner workings of the equipment associated with the watch station. Now I am not saying that an RO knew as much as a MM when it became necessary to repair a piece of equipment, but he knew how it worked, how to operate it, and the part it played in the successful operations of the plant.
A fully qualified RO was capable of standing all watch stations in a start up, shutdown, or steaming mode.
As to EM's qualifying as shutdown reactor watches (not the case in my day), I suspect it was all about manpower issues. Unlike all the other watch stations, the reactor watch (and charging station) had to be manned as long as there was fuel in the reactor.
As I have stated elsewhere, there is no technical reason other ratings could not qualify as a RO other then the Navy saying NO.
As to having a fun watch, I found EW ELINT (electronic surveillance and counter measures) watches to be more fun and challenging. It was especially rewarding when you detected an approaching submarine before SONAR did. One sweep of their radar was all it took, and you got them. (probably something not necessary these days)
Oh, another thing, back in the day, ET's IC's (RO's), MM's, and EM's frequently worked their rates outside of the nuclear program. As an ET, I served as an RO on Bainbridge, and as OE Divison LPO on Decatur. Also back then sea shore rotation was 2-3 years each, not the rotation those in the service now 'enjoy'.
Enough of an old man opining on the past.