Complex sentence: Project Grudge was a short-lived project by the U.S. Air Force to investigate Unidentified flying objects that succeeded Project Sign in February, 1949, and was then followed by Project Blue Book.
Split into simpler sentences: Project Grudge was a short-lived project by the U.S. Air Force to investigate Unidentified flying objects. Grudge succeeded Project Sign in February, 1949, and was then followed by Project Blue Book.