Until the early twenty-first century, their use was limited by the complexity of designing and controlling them.
ʌntˈɪl ðɪ ˈɜːli twˈɛntifˈɜːst sˈɛntʃɚɹi, ðɛɹ jˈuːs wʌz lˈɪmɪɾᵻd baɪ ðə kəmplˈɛksᵻɾi ʌv dɪzˈaɪnɪŋ ænd kəntɹˈoʊlɪŋ ðˌɛm.