Miranda Class (TOS Era)

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A lot of people have speculated that there were other classifications of ships in the service of Starfleet during the TOS era besides the Constitution class.  They further speculated that some of the ships we see in the movies or TMP era were probably refits of those TOS ships.  

Hence the idea for a TOS era Miranda Class.

Although we never see a TOS era version of this type of ship on screen, there is a reference to the USS Reliant in the Star Trek: The Original Series episode called "Court Martial" where the Reliant's registry is seen on the wall in the background of one of the scenes, indicating that she was in dock for repairs.  Using that as a point of reference, it can be rationalized that what we see in Star Trek II is in fact, a refit version of the ship, much like we are treated to a refit Constitution class in the movies.