Doctors in today's U.S. military receive commissions without any command training. If you enter as a licensed physician, your rank will typically begin at captain or major (Army/Air Force) or lieutenant or lieutenant commander (Navy), but it may be higher depending on where you are in your civilian career.
Yes but I'm not sure that tracks with Starfleet. Crusher and Troi had to do additional training to command the bridge but you don't jump from zero training to commanding the bridge. Command training and training on all ship's systems seems to be part of standard training for officers. Non-commissioned crew seem to just get systems training and develop leadership skills over time.
I'm certain that that was the intention with McCoy. TOS shows several times that he's unfamiliar with the more military aspects of Starfleet. He hasn't heard the Academy slang term "Dunsel" in "The Ultimate Computer." He's uncertain if confining Spock to his quarters is sufficient punishment for hijacking the ship in "The Menagerie." And he's demonstratively not as familiar with the regulations about another flag officer taking command as Spock and Decker are in "The Doomsday Machine." Although it's never stated outright, the implication is definitely that McCoy didn't attend the Academy and received his commission because of his medical degree. TNG went with the assumption that everyone in Starfleet went to the Academy.
Yeah but the Captain can specify anyone s/he likes to be officer of the deck and might put an ensign in charge when there isn't a crisis. All this tells us is that the Captain is in charge, like when Picard puts Geordi in charge when he's a Lt.jg.
On the issue of who's in command ...
I note that near the end of "Journey to Babel," Kirk is badly wounded but remains on the bridge as long as he can during the climactic crisis.
Once things calm down, Kirk says "Mister Chekov ... take over" as he slowly departs.
Spock is in sickbay, donating blood too his father. Scotty is busy below, keeping the ship together. Sulu is absent (I think he was hangin' out with John Wayne on a film set).
Lt. Uhura is clearly in the long shot as the captain exits. In fact, she's within three or four steps of the captain's chair. Yet, Kirk designates Chekov, who recently came aboard and who hasn't any stripes. I know that Kirk is wobbly, but it's still curious.
(I had prepared a screen grab, but for some reason I can't get it to display.)
https://imgur.com/a/KgeJztC
I think that's illustrated quite well in the series. In "Trouble with Tribbles", McCoy says to Spock, "I like them, better than I like you." At the end of "Operation Annihilate", McCoy tells Kirk (thinking Spock can't hear him) that Spock is "the best first officer in the fleet".
I wonder what the Lt. Unknown sitting at the helm did so that Kirk ignored him, too.
I wonder what the Lt. Unknown sitting at the helm did so that Kirk ignored him, too.
At least he wasn't appointed chief engineer. Nothing about this is unusual.
