Gah, I don't have the book with me to look it up for sure... but isn't there also some backstory in "Where No Man Has Gone Before" where Mitchell 'saved Jim's life' at some point during their pre-Enterprise service together? I can't recall the circumstance, but Mitchell got injured pushing Kirk out of the way amid some battle/threat.
If I'm remembering this correctly, then they have a bit of history beyond the Academy instructor/student days. That, or I'm confusing this story with another character from Kirk's past... hopefully someone can call up the facts.
MISSION:TREK's in-depth review of STAR TREK
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