We know the TOS Enterprise had tubes 2, 4, and 6, implying that there are also a 1, 3, and 5. But we are not told what arc they face nor are we told if there are tubes 7, 8, or 9. The Enterprise may well have had aft torpedoes. We are never explicitly told otherwise.
Sure, a bit of clarification then. The TOS Enterprise had 6 known forward tubes. All 6 were fired in
Elaan of Troyius.
The dialogue and the FX implies that all 6 tubes were used:
KIRK: Negative. His sensors will pick up our power increase. The more helpless he thinks we are, the closer he'll come. As he passes, I want to cut in warp drive. We'll pivot at warp two and bring all tubes to bear.
Of course it could also mean only
all facing tubes to bear. However the one time they should have fired from an aft tube (
The Changeling) they did not - which would imply the TOS Enterprise did not have any aft tube(s) since all 6 that were ever mentioned got used in
Elaan of Troyius.
The Enterprise episode Defiant? had a rear tube on the Connie but that's alternate universe territory so it may or may not be on any of the TOS Connies...
Not really. The
Defiant was native to the TOS episode "The Tholian Web." Granted it found its way into an alternate reality, the Mirror Universe, but that's not where it started. And some may argue that the whole of
Star Trek: Enterprise was set in an alternate timeline caused by the events of
Star Trek: First Contact, There's no reason to assume that the
Defiant was radically different compared to the TOS [/i]Enterprise[/i]. So, again, there may well have been aft arc torpedos on the TOS
E.
Actually there is reason to consider the Defiant at least different from the Enterprise. As pointed out above, the one time (if not others) where the Enterprise would've fired out of an aft tube, it did not. Plus, there has not been a mention of an aft torpedo tube during the entire run of TOS (and plus the refit E does not sport an aft tube either) which points to an Enterprise that most likely did not have an aft tube
As far as the TOS Defiant goes, it could've had an aft tube in TOS as it was never specified either way, although the Enterprise-A (considering it is a new build, or refit of another Connie) also does not have an aft tube so it would seem that any Connies during TOS that might have had an aft tube, did not retain it when refitted or newly built into the movie version.
Funny you should suggest that the Defiant is native to the TOS
The Tholian Web. Considering that the interphase space connected to multiple universes how could you be sure that the Defiant that appears in the ENT Mirror series is really the one from the TOS series? It could be from the ENT future universe (and thus be slightly different) given all the Temporal Cold war stuff that happened. So, for me at least, I'm a bit skeptical on the ENT version of the Defiant.
If you are aware of a TOS or TFS moment (not TNG+) where the TOS E had an indicated use of an aft tube or dialogue of such, I'm all ears.