User blog comment:Arden.tenjou/Explanation of the Title: "Shingeki no Kyojin"/@comment-179280-20140104022016

You seem not to have noticed that 「進撃の」 is treated as an adjective, because of the way it is written. The title doesn't mean "Giants of the advance", but "Giants that advance". The 「の」 here is marking that 「進撃」 is not a noun, hence your translation is incorrect just like the official title.