03/15/2007. Remarks by Jack McKillop: "Curtiss received an experimental contract from the Army to develop to night bombers to replace the NBS-1. This aircraft had a steel-tube fuselage instead of the wooden fuselage of the NBS-1 and a new and thicker airfoil. Curtiss built two XNBS-4s but was not awarded any production contracts for this new aircraft.

This was the first XNBS-4 and was delivered in May 1924 and surveyed in July 1930 with 717 hours on the airframe. On the engine cover the McCook Field Project Number "P-352" is visible."