During assembly, the second prototype XO-27 was converted to a bomber prototype, dubbed the XB-8. While the XB-8 was much faster than existing biplane bombers, it did not have the bomb capacity to be considered for production. Two YB-8s and 4 Y1B-8s were ordered, but these were changed mid-production to Y1O-27 configuration.
The wing of the XB-8 and XO-27 was built entirely from wood, although the fuselage was constructed of steel tubes covered with fabric with the exception of the nose which had a corrugated metal. They featured the first retractable landing gear ever fitted to an Army Air Corps bomber or observation craft. The undercarriage retracted electrically. Crew was three in tandem position.
It competed against a design submitted by Douglas Aircraft Company, the Y1B-7/XO-36. Both promised to greatly exceed the performance of the large biplane bombers then used by the Army Air Corps. However, the Douglas XB-7 was markedly better in performance than the XB-8, and no further versions of Fokker's aircraft were built.