This is the second, or S-II-F/D, or Facilities Checkout/Dynamic Test Stage, of the Saturn V launch vehicle. This stage of the rocket was not meant to fly but was used for ground tests pior to the actual flight tests. As in the flyable version of the Saturn V, the stage shown here is fitted with five J-2 rocket engines, all inoperable. The Dynamic Test version of the rocket was extremely important in Apollo program - it proved the validity of the vehicle's structural design. In its flyable form, the 363-foot long, 33-foot diameter operational version of the Saturn V rocket took a dozen astronauts toward the Moon during 1969-1972 and is considered one of the greatest engineering achievements in history. The second stage was transferred by NASA to the Smithsonian in 1975.