swagnerle

I´m one of the german civ players.. sorry for my bad english.... In the tech tree there is sometimes something like " 3 more techs vor the destroyer"... but what techs do i need to research. Is there a hint or a box where it is explained? Or I´m just a blind man? if it doesn´t exist please insert a hint box or something like this. If it already exist please give me a hi