The Junkers Ju 90 was a transport plane that were to be used by Lufthansa and the South African Airways. It was developed in 1936 to meet an Air Ministry specification for a long range bomber. The Junkers Ju 90 was an all metal aircraft with low wings.
The Junkers Ju 290 was basically an armed Ju 90 that was designed in 1940. The Ju 290 was also bigger than the Ju 90. The Ju 290 was touted as a replacement for the Fw 200 Condor. However it was never produced in enough quantities to replace the Condor.
In 1943 the Fw 200 was needing to be replaced quickly. The Ju 290 had additional armament installed. Radio equipment and radar were also added. This became the Ju 290 A-2.
There was a gondola that contained a 20 mm MG 151 and 13 mm MG 131.
There was a Trapoklappe, a hydraulically operated ramp, that was in the rear fuselage and could be opened in flight or if used on the ground could lift the plane for loading.
The Ju 290 had very sturdy undercarriage.
The Ju 390 had two additional undercarriage units due to its size.
In early 1944 some of the Ju 290s were modified to carry 6,000 gallons of fuel.