ɐkˈoːɹdɪŋ tʊ ɐ blˈuːpɹɪnt pɹəvˈaɪdᵻd ɪnðə kˈɑːmɪk bˈʊk dʒˈiː.ˈaɪ. dʒˈoʊ hˈæʃ twˈɛnti tˈuː, mˈɑːɹvəl sˈɪɹiz, ɪts ɹᵻbˈɪlt tə sˈɪks stˈoːɹiz ɪn dˈɛpθ, dᵻpˈɪktᵻd æz hˌævɪŋ bˌɪn dɪzˈaɪnd təbi mˈoːɹ dᵻfˈɛnsᵻbəl ænd ɪmpɹˈɛɡnəbəl.
According to a blueprint provided in the comic book (G.I. Joe #22, Marvel series), it's rebuilt to six stories in depth, depicted as having been designed to be more defensible and impregnable.