|Earth Pre-Federation Database - Neptune Class|
|Speed||approx. Warp 2|
|From Ex Astris Scientia - Bernd Schneider's Star Trek Site|
|This class of survey ships is older and slower than the NX class.
1) Tucker mentioned the Neptune class in a state of emotional stress in ENT: "Singularity" (these ships are using the same model of the captain's chair as Enterprise). But it is obvious that the ship class must exist.
2) The designation doesn't fit into the newly established scheme of simple letters. On the other hand, it is still possible that "NX" is only a preliminary class name and that simple letters are only used for civilian ships. Thus, Starfleet ships may already be named after the lead ship.
3) It is well possible that the Neptune class is one of the two unnamed ship designs of the pre-NX era.
Text from the Ex Astris Scientia - Bernd Schneider's Star Trek Site