pɹˈaɪɚ tə ðə sˈɛkənd wˈɜːld wˈɔːɹ, ðə hˈaɪɪst lˈɛvəl wʌz "mˈoʊst sˈiːkɹᵻt"; ɪt wʌz ɹᵻnˈeɪmd sˌoʊ ðæt bˈoʊθ ðə jˌuːkˈeɪ ænd jˈuː.ˈɛs. ˈɑːpɚɹˌeɪɾᵻd tʊ ɐ kənsˈɪstənt sˈɪstəm.
Prior to the Second World War, the highest level was "Most Secret"; it was renamed so that both the UK and U.S. operated to a consistent system.