USAF UFO program (1949-52). Successor to Project Sign; preceded Project Blue Book.
A primary-source link to Grudge appears in PURSUE Release 02: the file DOW-UAP-D017 on the Green Fireballs sightings at Sandia Base notes that some of those investigations fed into Project Grudge.
Connections
Project Sign · Project Blue Book · Legacy Program · Green Fireballs · Sandia Base · PURSUE · Estimate of the Situation 1948