Are all the men on ironborn longships freeborn fighters, or do you think some are thralls who solely row? We see Vic using such to Meereen with captured slaves he “freed”. And do you think all the regions were involved in Greyjoy’s Rebellion? If not, which ones weren’t? Did Jon presumably staying in KL mean the Vale wasn’t rallied? Did Doran not seek to build (fake) trust with the Iron Throne by sending levies? Did Mace only “provide” the Redwyne fleet? Did Hoster leave it to the Mallisters?

opinions-about-tiaras:

The ironborn definitely use thralls as rowers. They may or may not solely row, but they are certainly thralls.

From the Victarion preview chapter of TWOW:

The oarsmen were all big. One was a boy, one a brute, one a bastard’s
bastard. The Boy had been rowing for less than a year, the Brute for
twenty. They had names, but Victarion did not know them. One had come
from Lamentation, one from Sparrow Hawk, one from Spider Kiss. He could not be expected to know the names of every thrall who had ever pulled an oar in the Iron Fleet.

Victarion did not oft forgive a thrall for talking out of turn, but the
Boy was young, no more than twenty, and soon to die besides. 

If it made the three feel braver to believe they had a choice, let them
cling to that. Victarion cared little what they believed, they were only
thralls.

That strikes me as a case of the Ironborn social contract beginning to break down once you shift from the smaller-scale longships to actual warships, because otherwise the Ironborn very much separate out thrall’s work from freeborn work:

racefortheironthrone:

1. I think that usually there’s a pretty strict code that there’s thrall’s work and Ironborn’s work and the two should not be mixed. Hence why Euron’s crew is an aberration.
2. The Reach, the North, the Westerlands, the Riverlands, the Stormlands, and the Crownlands were definitely involved. We don’t hear anything about the Vale or Dorne tho. 

“Amongst the ironborn, only reaving and fishing were considered worthy work for free men. The endless stoop labor of farm and field was suitable only for thralls.” 

Incidentally, this also suggests that argument about the Ironborn having larger army #s are wrong, because if they have to resort to thralls to fill out the oars of a ship a third the size of mainlander warships, no way in hell they have 30,000 men under arms.