The MiG-23's predecessor, the MiG-21, was fast and agile, but limited in its operational capabilities by its primitive radar, short range, and limited weapons load (restricted in some aircraft to a pair of short-range R-3/K-13 (AA-2 "Atoll") air-to-air missiles). Work began on a replacement for the MiG-21 in the early 1960s. The new aircraft was required to have better performance and range than the MiG-21, while carrying more capable avionics and weapons including beyond-visual-range (BVR) missiles. A major design consideration was take-off and landing performance. The Soviet Air Force (VVS) demanded the new aircraft have a much shorter take-off run. Low-level speed and handling was also to be improved over the MiG-21. Manoeuvrability was not an urgent requirement. This led Mikoyan to consider two options: lift jets, to provide an additional lift component; and variable-geometry wings, which had been developed by TsAGI for both "clean-sheet" aircraft designs and adaptations of existing designs.