We'd definitely need new hardware and/or infrastructure to work without GPS. > before GPS, direct transatlantic flight weren’t generally possible I'm not sure

We'd definitely need new hardware and/or infrastructure to work without GPS. > before GPS, direct transatlantic flight weren’t generally possible I'm not sure what you mean by this. Commercial transatlantic flight picked up after WW2 in the 50s. By the 1970s it was fairly common. A lot of that came from rocketry research and INS.