I’ve noticed a recurring problem whenever I play Civ V. I usually send out one or two Scouts to explore and upon researching Optics, I find that these Scouts don’t receive the Embarkment promotion so they can’t cross sea tiles. However, every Scout that I create after researching Optics has Embarkment.
My work-around thus far has been just deleting the Scouts I have out to be replaced by new Scouts. Is there something I’m doing wrong such that my Scouts aren’t receiving the Embarkment promotion or is this “by design”?
In order for a unit created before Optics is researched to receive the embarkation promotion, it needs to first return to its home territory (doesn’t have to be a city; entering your own domain should suffice) or stations itself in one of your allies’ city-states. Once there, it can then embark/disembark wherever it wants to.
Interestingly I can’t seem to find this in Civpedia, but as Rilgon has mentioned in the comments, it is mentioned by your advisor when you research Optics.