The Fokker (Atlantic) XB-8 was ordered by the US Army as a bomber derivative of
the YO-27 observation aircraft design.
The second prototype YO-27 was converted
during assembly to a bomber configuration. The Douglas XB-7 was ordered at the same time and was a derivative of the YO-35 observation plane.
The XB-8 was much faster than the existing Keystone bombers already in service, but couldn't carry a heavy enough bomb load to be considered for production.
6 service test aircraft were ordered as YB-8 and Y1B-8, but all were delivered as Y1O-27s.