04/30/2008. Remarks by Walter van Tilborg: "Produced as a model 340-70
C-131B the aircraft was delivered to the USAF in 1954. Deregulated to test duties the aircraft was designated NC-131B, that changed to model 580
NC-131H when it was re-engined with two 3,750 shp Allison 501-D-13D turboprops and was fitted with larger tail surfaces.