Wikipedia link for Easton (and Parkinson) credit for GPS: https://en.m.wikipedia.org/wiki/Global_Positioning_System#:~:text=Bradford%20Parkinson%2C%20professor%20of%20aeronautics,with%20the%20rank%20of%20colonel.

Ee times article referencing FHSS and Nikola Tesla:

https://www.eetimes.com/a-short-history-of-spread-spectrum/