I wouldn't call Troi a primary bridge officer either.
Do remember that both of them would have advanced degrees to hold the positions that they're in. That alone would give them extra rank I would think.
There ws an episode where Troi had to take command after the ship was in an accident and she was the only officer there. (Picard was trapped in a turbolift with some kids) She was totally useless and O'Brien had to constantly tell her what to do.
Originally Posted by theapparatus
I know in ToS, it seemed to flip back and forth between Scotty and Sulu and both of them were seen to hold the bridge when Kirk and Spock were gone.
I'm pretty sure that Scotty was formally 3rd in the command chain. Sulu was given command of the bridge a couple of times but I think that was only when Scotty was on the away team or otherwise occupied with keeping the ship from exploding. There were doubtless a few occasions where he was passed-out drunk like any good Scotsman as well.
Data was second officer of the Enterprise-E, but Deanna Troi had a higher rank than he and was the highest ranking bridge officer after Picard and Riker. Troi was in command of the bridge while the Enterprise-E was traveling to the Briar Patch, and when Data left the bridge to head to the Scimitar. However, La Forge left the bridge with Data, and as chief engineer he may have been third officer.
I'd assume she wasn't considered a normal bridge officer but seemed to be above Crusher by this point in the Chain of Command, but under Picard, RIker, Data, and La Forge.
From what a friend was was in the navy once told me, medical personnel are considered outside the normal chain of command and will only take charge in an absolute emergency; save on hospital ships where captains are usually physicians themselves. ST seemed to base its protocols on the British/U.S. model by and large.
Last I knew (correct me if I'm wrong), the main purposes of the XO (First officer) are to take the "short" captain's orders and "flesh them out" for the entire crew, and is designated to take command if the Captain is incapacitated.
"Second officer" is the guy designated to fill in as XO if either the captain or primary XO is incapacitated. Since this is primarily an "emergency" position, and space on a ship is at a premium, it's all to easy to envision the "owner" of this post as being a senior department head when not being third in command...
And what I mean by "flesh out orders of the captain", remember the older navy shows? The ones where the Captain says "all ahead full", and the XO makes sure that the helm/navigation knows what direction "ahead" is and signals the engine room to build up the engines for a full speed push? I actually vaguely recall Riker doing this a couple of times in the shows...
However, since we don't get to see our BOffs in action, and especially incapacitated, I'm happy to stick with designating my second in an RP sense and not having a formal option to do so... Now, assigning a BOff as "third shift duty officer"...