What is "skyhook balloon"

Skyhook balloons were high-altitude balloons developed by Otto C. Winzen (1917–79) and General Mills, Inc. They were used by the United States Navy Office of Naval Research (ONR) in the late 1940s and 1950s for atmospheric research, especially for constant-level meteorological observations at very high altitudes. Instruments like the Cherenkov detector were first used on Skyhook balloons.