Not much information about this project has survived. It was based on the Me 309 but with the engine located behind a pressurized cockpit, much in a similar manner as the US BellP-39 Airacobra.
The engine was a Daimler-Benz DB 605B driving a three-blade propeller and armament was to consist of two 13 mm (.51 in) MG 131 machine guns and two 20 mm MG 151/20 cannons. The tricycle landing gear from the Me 309 was retained, which worked better on the 509 due to the lower weight on the nosewheel - the Me 309's front landing gear had collapsed during trials. The smaller nose would have improved visibility. The project was cancelled along with the Me 309, but the Japanese made a similar aircraft, the Yokosuka R2YKeiun, which suffered from engine overheating.