They are listed at combinedfleet as Prisoner of War Relief Supply Ships.
Functionally it doesn't matter even a little if they carried POWs or not. They carried supplies for POWs at the very least, and were not to be sunk. What matters is that the paint measure existed. "POW" exists as nothing more than the name attached to the skin. That's it we called them POW because naming the skin "Prisoner of War Relief Supply Ship" is rather long. They appear in late '43, and if you see
one in every 50 campaigns I'll be surprised, frankly.
From the player perspective, it's the fact that they are not legitimate targets that matters. If they carry POWs or just supplies for POWs... doesn't matter, player should still get a renown hit if he sinks 'em, no? The way the skins are set up, they could be white (hospital) and take a renown hit. They could be green with crosses, and then they are these pow supply ships, again, should not hit them. Since they are so incredibly rare anyway, we could have some in grey paint, and you'd STILL get a renown hit if you sank one. Tough luck—that would be a good sinking, then presumably after you RTB ONI figures out via sigint, diplomatic complaints, whatever, that it was filled with your own guys.
I added "supply" between "POW" and "ship" in the first post for ya
I realized some of these posts might seem pointed, if they do I apologize, I appreciate the feedback and research a great deal, gerritj9. <S>