This is a view of the Saturn V instrument unit (IU) being manufactured in the east high bay at International Business Machines (IBM) in Huntsville, Alabama. IBM is a prime contractor for development and fabrication of the IU. The IU is vital to the proper flight of the vehicle. It contains navigation, guidance, control, and sequencing equipment for the launch vehicle. Three feet tall, twenty-one feet in diameter, and weighing about 4,000 pounds, the IU is mounted atop the S-IVB (third) stage, between the S-IVB stage and the Apollo spacecraft.