11/15/2020. Remarks by Johan Visschedijk: "In 1931, the first P-6A was converted to the XP-6D with a side-mounted turbo-supercharger, and in 1932, all remaining YP-6 and P-6A aircraft (two had crashed) were converted at the Fairfield Air Depot to the same standard with Form F-2F superchargers; they then became P-6Ds and were assigned to Langley Field, Virginia, for service trials."