Vipre:
Watch every episode of and every movie of and if you like read every book about or comic book about Star Treks TOS/TMP Constitution class starship. You'll find two things, one is every weapon ever mentioned or accepted as being there has been fired at least once, and the other is nobody in command during a fight has ever ordered the rear torpedo tube fired because there wasn't one.
Sorry to disappoint. Diane Duane's first Rihannsu book,
'My Enemy, My Ally' has the
Enterprise firing aft torpedoes while fighting beside Ael's
Bloodwing against 4 Romulan ships.
My take on cannon is the same as Larry's:
If it has been seen on screen, it is 90% "The Way It Is", with 10% wiggle room to fudge for poor story-writing and lack of continuity for whatever reason (lack of budget, no time to check Memory Alpha, etc.)
If it hasn't been seen on screen, it is not canon. But if it hasn't been seen on screen, it doesn't mean it might not be
later on. The E-D has two--
two!--torpedo tubes; fore and aft. But the forward one can burst-fire at least 4 at once (
'TNG: Yesterday's Enterprise' - torpedoes split apart
after launching), and I have a clip of about 10 being fired inside of 2 seconds. It doesn't need to be armed with 10 tubes. But 2 tubes sounds wimpy. So, the E-E has 12 tubes firing more like the original refit
Enterprise and
Reliant.
Semi-canon schematics from backstage sources are fantastic as it conveys the original intent, but they will still be replaced if the next set of producers want something different. Fanon schematics will do when nothing else is known as they help fill in the blanks. I love my fanon Miranda-class deck plans. But when something new is shown on screen, it is automatically canon.
I personally would prefer Judith and Garfield Reeves-Stevens' book
'Federation' as the canon version of Zephram Cochrane's life, and Margaret Wander Bonano's
'Strangers From the Sky' as the canon version of Earth's First Contact. Both are fantastic, entertaining stories, but both have since been supplanted by
'Star Trek VIII: First Contact'. Arguably the best of the TNG movies, but I still prefer the books.
If we agree that 90% of what is seen on screen is canon for Trek, barring budget constraints and inattention to continuity issues, then that is the "Truth" for Star Trek. And the "Truth" is always unwelcome as it destroys someone else's closely cherished "in the absence of hard datas speculations.
As my wife says, "Put on your big girl panties and deal with it!"