This came up on a KEYSTONE search- entertaining reading-
Documents Reveal How the NSA Cracked the Kryptos Sculpture Years Before the CIA
According to a former Defense Department cryptanalyst who spoke with Wired, McDaniels was responsible for cracking section three and did it in just six hours lying on his living room couch with paper and pencil after coming home exhausted one day from playing volleyball. McDaniels is now retired from the NSA and declined to speak with Wired about his work on the sculpture. But the source told Wired that McDaniels had been out all day playing volleyball and came home around 10pm.
"He plopped down on the couch in the living room, picked up his draft notes for K3," the source said. "He had tinkered with it before but could never get into it. He knew it was just basic transposition, so he started with the letter Q and [the letter U after it] and found there were five instances of the letter U, and he just tried all five of those. Then he had to try every other vowel that came after and he finally found something that broke it. By then it was about 4am and he was done."
https://www.wired.com/2013/07/nsa-cracked-kryptos-before-cia/