ðə fˈɜːst flˈaɪɪŋ jˈuːnɪt ˈɛs twˈɛnti wˈʌn wʌz ɪnˈɪʃəli tˈɛstᵻd ɔnðə vˈɑːlɡɚ ɹˈɪvɚɹ ɪnðɪ ˈɔːɾʌm ʌv nˈaɪntiːnhˈʌndɹɪd sˈɛvənti tˈuː, ænd ðə nˈɛkst jˈɪɹ dɪsmˈæntəld ænd tɹænspˈoːɹɾᵻd tə ðə kˈæspiən sˈiː fɔːɹ kəntˈɪnjuːd tˈɛstɪŋ.
The first flying unit (S-21) was initially tested on the Volga River in the autumn of 1972, and the next year dismantled and transported to the Caspian Sea for continued testing.