[Hector, tamer of horses]

I have summoned a Sea king and his Troll court. It says that the Troll King can enable units with him to breathe underwater. How many? I put a Crown of Command on him hoping that he could enable a big pile of units to go with him underwater. But it keeps dumping them and indicating that only a portion of the units can go. Far less than the command limit.

What am I missing?