Some of the techs, for the ships enabled by that tech, list the same ship twice. For example, Stinger II lists "Attacker", "Fighter", and then "Attackerr" again. By the way, despite researching all the techs I could find that listed fighter or attacker as ships enabled by that tech, I have yet to see those ship classes showing up in my shipyard. Is that a bug, or are there yet more techs I have to complete to enable those ships?