Dr. Dave Greenwalt is a fictional United States Air Force Global Positioning System (GPS) expert. A supporting character in the 1997 film Tomorrow Never Dies, he is portrayed by Canadian actor Colin Stinton.
After recovering a stolen GPS encoder from media mogul Elliot Carver, 007 brings the device to the Americans for examination. Performing tests on the encoder, Greenwalt discovers that Carver tampered with the device's timing chip, sending the British ship HMS Devonshire off course and into Chinese waters. Bond then asks him to figure out exactly where the ship sank.