Saturn-Shuttle

The Saturn-Shuttle was a preliminary concept of launching the Space [Shuttle orbiter] using a modified version of the first stage of the Saturn V rocket. It was studied and considered in 1971–1972.

Description

An interstage would be fitted on top of the S-IC stage to support the external tank in the space occupied by the S-II stage in the Saturn V. It was an alternative to the SRBs.
Some studies proposed the addition of wings to the S-IC stage, which would allow the booster to fly back to the Kennedy Space Center, where technicians would then refurbish the booster for another flight, whether in its entirety or just the tankage.
The Shuttle would handle space station logistics, while the Saturn V would launch components. This would have allowed the International Space Station, using a Skylab or Mir configuration with both U.S. and Russian docking ports, to have been lifted with just a handful of launches. However, it was ultimately rejected on basis of cost.