A manned Venus flyby was considered by NASA in the mid 1960s as part of the Apollo Applications Program, using hardware derived from the Apollo program. Launch would take place on October 31, 1973, with a Venus flyby on March 3, 1974 and return to Earth on December 1, 1974.
By means of Saturn V technology, would be sent three men toward the interior of the Solar System in a journey of a year of duration, flyby Venus. The spacecraft, similar in design to that later would be sent to the space like the Skylab space station, it was thought so that the astronauts could travel "comfortably" during so much time, returning home in the same way to as the lunar Apollo.
The S-IVB stage would be a 'wet workshop' similar to Skylab, first using the S-IVB engine to launch the mission on course to Venus, and then vented of any remaining fuel to serve as home for the crew for the duration of the mission. The Apollo SM engine would be used for course corrections on the way to Venus and back to Earth, and for a braking burn before the Command Module re-entered Earth's atmosphere.
As a bonus to the mission, a flyby of 500 km above the Earth that SIVB, approaching the planet Mercury 4 months later (exactly one year after the encounter with Venus).