The Ju 390 came along when intense effort and German wartime philosophy was still geared towards the use of medium bombers and fighter/bomber hybrids. As such, full resources were never really delegated to the project en mass. The Ju 390 basically was the Ju 290 airframe with extensions fitted into the wings to lengthen them and accommodate the added powerplants. Furthermore, lengthening of the base fuselage also took place in this new design.
First flight was recorded on October 20, 1943 with good results. The system performed admirably well for its size and was designated as the Ju 390 A-1. An initial order of 26 such aircraft were ordered into production only to see the project cancelled in the middle of 1944 in an effort to allocate resources and design time to other more pressing projects.
The idea of a transatlantic New York Bomber was an intriguing one. Obviously more of a psychological tool of terror than a practical effort, the Ju 390 was to hit at the heart of New York City in a way that the Luftwaffe shown it could do to Londoners in England during the war. The end result might have been mixed, as it could have either demoralized the American war effort if the bombers were truly effective or strengthen their resolve.
A disputed flight of a test Ju 390 reaching New York is said to have occurred but there is evidence for both sides to accept or dispute this claim. Nevertheless, the 2 versions that were built made the 32 hour flight most definitely possible. The fact that such an aircraft could approach through the Atlantic undetected leaves some to disagree with such a feat.