I was researching a B-29 crash that my grandfather was in during the Korean War, and he was listed as the IVO on the flight. I couldn't find what that abbreviation meant, nor could I find some of the others for crewmen on the flight: CFC and VC. There was an IP on the flight, which is an Instructor Pilot, so I was wondering if my grandfather was an Instructor V-something Officer. Also the crash happened at night, if that's relevant.
I reached out to the Korean War Education Site, who were quite courteous and responsive. I will quote their answer below (I have removed personal information since they didn't grant permission to use names).
Can’t verify but seem to recall that the VO was the radar operator. RO would have been the Radio Operator, thus the V. The “I” would indicate Instructor, so IVO would be the instructor radar operator. Don’t recall ever using the VC designation. It could be a either a command or crew chief position. Rank would help narrow it. I also believe I remember that the crash occurred at night, followed by an explosion the shook our hut. When we saw the flames, everyone who witnessed it agreed that there could be no survivors. We were happily astonished when we learned there were no fatalities. Apparently one of the crew died later.The Korean War Educator