The S-6 was development of the S-3 with two forward facing guns above the propeller arc. Guns may not have been operational but mounted to test weight and balance. One S-6 was delivered to the US Army as serial 492. The S-6 was built at the experimental factory at Garden City, Long Island. The photo appears to be at Curtiss' Buffalo airfield as the buildings in the background appear in photos taken the year before Garden City opened. Photo from: National Archives at College Park, Maryland