Unit availability in scenarios

I recently joined a GoT game playing SM because they had bomber equivelant units, but when I joined I discovered that the bomber-type units were locked from me. I was SM with no air force. What upgrade would unlock them & why didn't my strat open it automatically? SM should have also opened the air stealth, but failed.

The map makers probably made them land units.

This is because they were rare-only air units.