The F-8 Digital Fly-By-Wire aircraft had its hydro-mechanical control systems replaced by an Apollo Guidance Computer for the first such control system to fly.

This illustration shows the major components of the instrument unit (IU). Developed and manufactured by International Business Machines, the IU is 3 feet high and 21 feet in diameter and mounted atop an S-IVB, between the third stage and the Apollo spacecraft. It contained the computers, all guidance, control, and sequencing equipment to keep the the launch vehicle properly functioning and on its course. The IU was essentially the same in both the Saturn IB and the Saturn V.