...If such a thing even exists. We have discussed the concept before, and there doesn't seem to be any plausible demarcation of a mission of this particular length (in the material of TOS or in the TOS-describing material added by the spinoffs): it's not bookended by port calls, refuelings, or by location or assignment changes. It seems to merely mark the length of Kirk's time at starship command out there ex post facto
. And not all of it was spent in exceptional deep space; plenty involved operations near starbases frequented by other Starfleet assets.
It's quite difficult to imagine that being a star ship skipper for five years would be exceptional as such... Yet the "five year mission" of the Enterprise
can't plausibly mean much else than a retrospective highlighting of those five years when Jim Kirk commanded her. And that doesn't really make either him or her particularly special (even though in combination, and in retrospect, the two become legend).
Much of "Court Martial" hinges on Kirk being special. Much of it is difficult to justify. Starfleet seems awfully small when so many of Kirk's old mates amass at SB 11 by accident, yet also awfully big when chance brings such large numbers of "special assets" such as star ships to the base. Something has to give - and we could always use this as leverage to force one interpretation of "star ship status" or another.