Wikipedia
The Saturn-Shuttle was a preliminary concept of launching the Space Shuttle orbiter using the Saturn V rocket.
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, so that NASA would have been able to steer completely away from solid rockets.
The addition of wings on the S-IC stage would allow the booster to fly back to the Kennedy Space Center, where technicians would then refurbish the booster (by replacing only the five F-1 engines and reusing the tanks and other hardware for later flights).
The Shuttle would handle space station logistics, while 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. The Saturn-Shuttle concept also would have eliminated the Space shuttle solid rocket boosters that ultimately precipitated the Space Shuttle Challenger accident in 1986.