A-ok (also, A-okay or A-OK /ˌeɪ.oʊˈkeɪ/) is a more intensive word form of the English term OK.
US Air Force Lt. Col. John "Shorty" Powers popularized the expression "A-ok" while NASA's public affairs officer for Project Mercury, and was reported as attributing it to astronaut Alan Shepard during his Freedom 7 flight. However, the NASA publication This New Ocean: A History of Project Mercury says in a footnote: "A replay of the flight voice communications tape disclosed that Shepard himself did not use the term." and that "Tecwyn Roberts of STG and Capt. Henry E. Clements of the Air Force had used 'A.OK' frequently in reports written more than four months before the Shepard flight." Apparently, the first documented use of "A-ok" is contained within a memo from that Tecwyn Roberts, a Flight Dynamics Officer, to Flight Director (entitled "Report on Test 3805", dated Feb 2, 1961) in penciled notes on the countdown of MR-2 (Mercury-Redstone 2), dated Jan[uary] 31, 1961. In his book The Right Stuff author Tom Wolfe wrote that Powers had borrowed it from NASA engineers who used it during radio transmission tests because "the sharper sound of A cut through the static better than O".
The phrase can be accompanied by, or substituted with, the A-OK sign.
Note: The phrase "A-OK" has already been in use in 1952 in an advertisement by Midvac Steels which titles "A-OK for tomorrow's missile demands" (see "The Golden Age of Advertising - the 50s", p. 57, Ed. Jim Heimann, Taschen 2005).