The Ministry of Aviation worked on the plans from about 1937. Design proposals were made at the great German aircraft manufacturers at the beginning of the Second World War - long before the US entered the war. The most promising candidates were based on conventional principles of aircraft design and would have been very similar in appearance, design and performance to the heavy Allied bombers of that time: Heinkel He 277 (based on He 177) Messerschmitt Me 264 (a completely new design) Focke-Wulf Fw 300 (based on the Fw 200) Focke-Wulf Ta 400 (a completely new design) Junkers Ju 390 (based on the Ju 290 ) Prototypes of the Me 264 were built, but it was the Ju 390 that was selected for production. Only two prototypes were constructed before the program was discontinued. [2] The strategy was to let the heavy bombers start from the Azores. From there it is about 4,000 km to New York City. The German Reich tried to lease a base in Azores from neutral Portugal. [3] Ultimately, the Portuguese leader António de Oliveira Salazar agreed in 1944 with the British