Apollo4 and Apollo6 were "A" missions, tests of the SaturnV launch vehicle using an uncrewed Block I production model of the command and service module (CSM) in Earth orbit.
ɐpˈɑːloʊ fˈoːɹ ænd ɐpˈɑːloʊ sˈɪks wɜː "ˈeɪ" mˈɪʃənz, tˈɛsts ʌvðə sˈæɾɜːn vˈiː lˈɑːntʃ vˈiəkəl jˈuːzɪŋ ɐn ʌŋkɹˈuːd blˈɑːk aɪ pɹədˈʌkʃən mˈɑːdəl ʌvðə kəmˈænd ænd sˈɜːvɪs mˈɑːdʒuːl sˌiːˌɛsˈɛm ɪn ˈɜːθ ˈɔːɹbɪt.