David Shaw, I think, did a study in 2007 comparing the TOS/TMP Enterprise
s and how one could have flowed into the other. His conclusions (which I've boiled down) were:
"In 1978, there were NO accurate plans [of the TOS Enterprise
] on hand when the movie version was being designed...the designers [Andrew Probert & Co.] started with Matt Jefferies' Phase II plans. The Phase II Enterprise
to be a slightly upgraded version of the starship we saw in TOS, [but the designers inadvertently] further exaggerated [basic structural] changes that [Jefferies himself made, and] thought would be unnoticeable in the Phase II Enterprise
[since most of the exterior details would be the same].
"So yes, the TMP Enterprise
IS a refit/upgrade of the TOS Enterprise
- but the production designers didn't START with the Enterprise
we saw in TOS. The end result is that when the TMP Enterprise
is held up alongside the TOS Enterprise
, we see no clear-cut upgrade from one to the other. But when Jefferies' Phase II changes [to the TOS ship's basic lines before anything was 'upgraded'] are taken into account, the upgrade path becomes quite clear."