I read somewhere that Thomas Jefferson developed a cypher method that could not be broken until WWII computers but the documentation lay in the National Archive, never used.
Wikipedia has a nice write up here:
https://en.wikipedia.org/wiki/Jefferson_disk
The Jefferson disk was the basis for the US “M-94” cipher machine, which was introduced in 1922 and used by the Army until 1942. The Germans broke it by 1944.