There’s a recurring pattern in the excellent Posideon’s Spear by Christan Cameron, where Arimnestos of Plataea takes a bunch of regular people who are serving him as oarsmen, and trains them into light infantry (so they're more like a crew in the very ancient style, where pentekonters would be filled with warrior-oarsmen rather than having dedicated marines). They start out as fishermen, shepherds, farmers and craftsmen, but finish capable warriors rather than mere rabble. It begins with arming them and making them practise every night when they beach the ship, and is cemented when they are taken into combat for real.
I’m going to leave the equipment aspect aside, because that isn’t hugely relevant, and is easy to deal with. What it looks like to me is that Normal Men/0th level characters are being turned en masse into 1st level ones. Or are they just going from non-combatant Normal Men to the light infantry troop type? Does that have any meaningful impact?
According to Manual of Arms, it takes a month, which seems pretty reasonable. Also included in that is teaching them to fight as a formation, rather than a disordered mob. How is that represented – I should have a look at D@W: Battles – I’m guessing there’s a loose formation and they can fight in closer order? Perhaps it takes a year of experience rowing and fighting for some of them to gain 1st level? If they all become 1st level characters (most likely Fighters) how does that impact the level demography? Does it even matter?
They’re also turned into proper oarsmen as they go, which would seem to be acquiring the Labour (Oarsman) Proficiency to me, possibly Endurance and Seasoned Voyager (a naval version of Adventuring, covering knowing how to scrounge firewood and food, build a fire, set a watch on a beachside camp, not make lubberly mistakes aboard ship). However, if they already have a full stack of Proficiencies from their mundane life before the career change, how would they acquire these? Or would we assume that most unskilled Normal Men probably have no more than one or two Proficiencies out of their allotted four?
I guess this all ties into the problem D&D has generally with training. If you took a bunch of slaves, freed them, fed them properly, exercised them and trained them as oarsmen, they should get stronger and fitter. That would be increases in Str and Con (perhaps some of which might be restoring lost Str/Con from being badly treated in captivitity), but how would you model that? I could see gaining 2 or even 4 points to each (a trained rower is stronger than an ordinary person in many trades), though that wouldn’t happen in a month, more like 3-6 months. It would also decline given long enough out of training, but are we getting into pointlessly complex territory here?