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.
Upon examining the device, Greenwalt explains that Carver's associate had tampered with the timing chip, sending the British ship HMS Devonshire off-course and into Chinese territorial waters, where the ship was sunk and a Chinese MiG jet shot down by Carver's ship to incite tensions between the two countries. As a result of the doctor's expertise, he was able to confirm where the Devonshire actually was based on data from the encoder.
Greenwalt later accompanied Wade and Bond aboard an American transport craft, which the latter H.A.L.O. jumped from while above Vietnamese territorial waters. The doctor confirmed to Wade and another officer that Bond's equipment was stamped with American insignia, much to the consternation of the two.