I don’t know about Subotai’s, because if the subs would need to submerge, then 2 subs attacking 1 AC 2 ftr would allow the 2 ftr to defend, because the subs won’t dive whilst trying to destroy the AC. But ftrs aren’t allowed to shoot at subs, so what happens than?
I have another question though:
The rules state that, during an amphibious assault, “a transport must either offload all units that were loaded during the Combat Move phase or retreat during sea combat. It may also offload any number of units owned by the transport’s power that already were on the board at the start of the turn.”
Does this mean that if I load 2 inf in turn N, and I amphibiously assault some territory in turn N+1, that I don’t have to disembark both of my inf, but that 1 inf may stay in the transport? (because they weren’t loaded during the Combat Move phase)