The Me 309 was originally designed to be the definitive successor to the Me 109.
The new fighter had many novel features, such as tricycle landing gear (with a nosegear strut that twisted through 90? during retraction, to a "flat" orientation under the engine) and a pressurized cockpit, which would have given it more comfortable and effective high-altitude performance. Each of the new features was first tested on a number of Bf 109F airframes, the V23 having a ventral radiator, the V31 with a radiator and tricycle landing gear, and the V30 having a pressurized cockpit.
The V-4 was armed with four MG 131, two MK 108 and a MG 151/20. This heavy armament led to a decrease in speed that was unacceptable for a fighter. In the autumn of 1943 the Me-309 program was officially terminated.
However, the 309 could be out turned by the Bf 109G and was judged inferior to the Fw 190D and never reached production.
In all four prototypes were produced.