@lowqualityfacts There is a wonderful history of the development and use of the U-2 and SR-71 (Oxcart) called "The U-2 and Oxcart programs: 1954 - 1974". Doc C05653421. Declassified 16 Jan 2011. Has a historic/histerical note on the US Air Force's attempt at launching balloons to float/fly over Russia.