Proyecto Grudge (1949)

Segundo estudio oficial de la USAF, conocido por su postura desestimadora; antecedió a Libro Azul.

Project Grudge was a short-lived project by the U.S. Air Force (USAF) to investigate unidentified flying objects (UFOs). Grudge succeeded Project Sign in February 1949, and formally ended in December 1949. It was followed by Project Blue Book in 1952.