"The Hawkeye world has the same catch-22 attitude with FOs in the right seat; they don't train FOs to be copilots because FOs aren't trained to be copilots."
At one time (many years ago) we tried an experiment on both coasts with NFO Co-pilots (VAw-122 and -126 on the East coast, -114 and -116, I think, on the West). Criteria was one had to be a second tour mission cdr, go through the FRS syllabus and get NATOPS qual'd by the FRS. It was supposed to be for day/VMC off the ship, but I went for 5 traps before I had my first day VMC right-seat trap (lots of marginal pinkies...). First flight was something like
this
In VAW-126, our take (and ditto in VAW-122) was along the lines that it was kind of useful, though not so for the original reason (spelling pilots on the flight sched rotation for around the clock ops conducted over the span of weeks/months) - you ended up wearing out the senior MC's in the process and it was hard hewing to the day/VMC deal (see above). The big plus was it pulled the NFO's mindset out of the b/end of the airplane and gave them a better understanding of it's mechanics (especially engines) if they weren't in maintenance for their ground jobs, and something of an appreciation for the mental gymnastics the front end had to got through w/o a scope in front of them. All those fun things like playing marshall for HCR's (Hummer Controlled Recoveries), strike for EMCON ops, etc. It also gave you an appreciation for a triple cycle w/o a working autopilot...
Nevertheless, as much as the squadrons seemed to like it - the "Powers That Be" at the wing hated it and the program died not long afterwards (ca. 89/90 IIRC).