hɪstˈɔːɹɪkli ðɪs wʌz dˈʌn wɪð ɐ mˈɑːdᵻfˌaɪd vˈælvɪbˌɑːdi ænd ɐ sˈɪŋɡəl sˈoʊlənˌɔɪd ɐlˈɔŋ wɪð sˌʌm ɪntˈɜːnəl tɹænsmˈɪʃən mˌɑːdɪfɪkˈeɪʃənz, lˈaɪk ɪŋkɹˈiːsɪŋ lˈaɪn pɹˈɛʃɚ, ænd ɹᵻmˈuːvɪŋ ˈɛndʒɪn bɹˈeɪkɪŋ bˈænd ænd bˈiːfɪŋ ˌʌp ɪntˈɜːnəl kəmpˈoʊnənts tə wɪðstˈænd ðə hˈɑːɹʃ lˈɔːntʃᵻz, ðə vˈælvɪbˌɑːdi ænd sˈoʊlənˌɔɪd wɛn ˈæktᵻvˌeɪɾᵻd ɐlˈaʊz haɪdɹˈɔːlɪk flˈuːɪd tʊ ɛŋɡˈeɪdʒ bˈoʊθ fˈɔːɹwɚd ænd ɹᵻvˈɜːs sˌaɪməltˈeɪniəsli wɛn vˈoʊltɪdʒ ɪz ɐplˈaɪd baɪ ðə dɹˈaɪvɚ wɪð ɐ mˈoʊməntˌɛɹi bˈʌʔn̩, ˌɔn mˈɛni ˌiːsˌiːjˈuː kəntɹˈoʊld vˈiəkəlz, ðɪs ɪz jˈuːʒuːəli dˈʌn wɪð ɐn ᵻlɛktɹˈɑːnɪk kəntɹˈoʊl sˈoʊlənˌɔɪd jˈuːzd tə sˈɛnd ðɪ ˌiːsˌiːjˈuː, ænd tˌiːsˌiːˈɛm ɐ dᵻɹˈɛktɪv sˈɪɡnəl.
Historically this was done with a modified valvebody and a single solenoid along with some internal transmission modifications, like increasing line pressure, and removing engine braking band and beefing up internal components to withstand the harsh launches, the valvebody and solenoid when activated allows hydraulic fluid to engage both forward and reverse simultaneously when voltage is applied by the driver with a momentary button, on many ECU controlled vehicles, this is usually done with an electronic control solenoid used to send the ECU, and TCM a directive signal.