Clearly, Gene spent the summer sprucing up the series bible. The Federation is now in place, and "non-interference" starts to come up, but it still takes them a while to get to having a Prime Directive. The progression is kindof hard to chart, since I'm guessing the production order, which is somewhat out of sync with the airing order, may have little or nothing to do with the order in which the episodes were written/conceived -- I'm told Omega Glory was actually written fairly early in the game (Gene evidently thought about using this one for the 2nd pilot but then came to his senses; good move, Gene).
Anyway, here's the progression I see:
- "Friday's Child" -- they beam straight in to the campsite in full uniform, showing their phasers at the first sign of trouble, and when those get confiscated, rescuing the High Tier's kid and introducing the bow and arrow ("should have as much impact on these people as gunpowder") is all in a day's work. Not there yet.
- "A Private Little War" -- Kirk, on his previous visit, had made a recommendation that the natives be left alone and allowed to progress at their own pace. The introduction (by the Klingons) of cold-rolled steel and rifle barrels is referred to as a "treaty violation"
-- and wow does that pro-Vietnam-War message really fall flat today.
- "Omega Glory" -- Beaming straight into a primitive village and making yourself out to be gods from the sky: No problemo.
Using your phasers to fight off a Yang attack: violation of Capt. Tracy's "oath as a Starfleet officer". Which suggests to me that the content of the oath might as well be, "I solemnly swear that I will not mow down thousands of people with my phaser", a worthy thought but a bit narrow as notions of "non-interference" go.
- "A Piece of the Action" -- leaving behind book on Chicago mobs is deemed bad, but it seems anything goes for the cleanup phase (sure, we'll randomly beam people around and phaser a whole city block just for grins...)
- "Patterns of Force" -- somebody leaves behind Mein Kampf; virtually the same problem, but now, coming in with guns blazing is evidently no longer allowed.
- "Bread and Circuses" -- the last-aired show of the season contains the first bona fide reference to a Federation "Prime Directive". The contrast with "A Taste of Armageddon" is amazing; here we have almost the exact same situation (Hi. Please call your ship and order the rest of your crew to beam down so that we can kill them all. kthnxbye...); Proconsul even remarks on how phasering the planet into smoking glass is not an option (... hm... would you want to bet your entire world on the strength of somebody else's Prime Directive? I wouldn't. Just saying...)
- Apollo: toast;
- Sargon & friends: toast;
- Kolob and Sylvia: toast;
- Vampire Cloud Thingie: toast;
- Jack the Ripper: toast;
- Giant Energy-sucking Amoeba Thingie: toast;
- People who built the Doomsday Machine: toast before the episode even started;
- Nomad: toast;
- Zephram Cochrane's girlfriend: toast in a few more decades;
- Kelvans: likewise
...and then, of course, the first episode aired that actually used it was "Enterprise Incident" where it was a Romulan ship. So that line about "Romulans now using Klingon design" must have been especially confusing to the first-run viewers in 1968, since at the point they were seeing it, they hadn't actually seen a Klingon ship before. Buh...)