ðɪ ˈɛkoʊ aɪklˈæs sˈʌbmɚɹˌiːnz wɜːɹ ɪŋkˈeɪpəbəl ʌv ɐkˈɑːmədˌeɪɾɪŋ ðə tˈɑːɹɡɪɾɪŋ ɹˈeɪdɑːɹ fɚðɪ ˈæntaɪʃˈɪp vˈɜːʒən, ænd wɜː nˌɑːt ɪkwˈɪpt wɪð mˈɪsəlz ˈæftɚ ðə lˈændɐtˈæk vˈɛɹiənt wʌz wɪθdɹˈɔːn, pɹˈɑːbəbli ɪnðə mˈɪd nˈaɪntiːnhˈʌndɹɪd sˈɪksti z wɛn səfˈɪʃənt nˈuːklɪɹpˈaʊɚd bɐlˈɪstɪk mˈɪsəl sˈʌbmɚɹˌiːnz ˌɛsˌɛsbˈiːˌɛnˈɛs bɪkˌeɪm ɐvˈeɪləbəl.
The Echo I-class submarines were incapable of accommodating the targeting radar for the anti-ship version, and were not equipped with missiles after the land-attack variant was withdrawn, probably in the mid-1960s when sufficient nuclear-powered ballistic missile submarines (SSBNs) became available.