The Saturn V’s control system was housed inside and also referred to as the Instrument Unit (IU). Marshall Space Flight Centers Astrionics Laboratory categorized the IU as the “brain” and “nerve center” of Saturn V.
“The S-II stage was a nightmare the minute it was conceived, and it only got worse from there. During the course of its creation, it would grind up people and careers the way the transcontinental railway devoured laborers. Though the methods and materials used to build the S-II were reasonably well known, nobody had ever tried to apply them on such a titanic scale. Originally, it was to be somewhere around 8 stores tall with a diameter of 22 feet, but the width ballooned from there to 27 feet before the contract was even signed, then to 30, and finally to 33 feet. And all the while as the size of thing increased, NASA was trimming the allowable weight.” Harrison Storms of NAA.
Apollo Saturn 201 employed the Saturn IB launch vehicle, which was the up-rated version of the Saturn I rocket flown in ten earlier Saturn-Apollo missions. It featured an upgrade of the first stage engines to increase thrust from 1,500,000 lb-ft of thrust to 1,600,000 lb-ft. The second stage was the S-IVB. This stage used a new liquid hydrogen-burning J-2 engine which would also be used on the S-II second stage of the Saturn V lunar launch vehicle…
Toward the end of January 1967, it was revealed that Lunar Module 1 would not reach the Cape in February, as expected. This meant, the moon landing might be delayed because the lander was not ready. But the mission planners could not wait for the Apollo engineers to iron out all the problems. They had to plan for a landing in 1969 and hope that the hardware would catch up with them.