The S-IC was composed of five major subsections. The largest and heaviest single component of the S-IC was the thrust structure, with a mass of . It was designed to support the thrust of the five engines and redistribute it evenly across the base of the rocket. There were four anchors that held down the rocket as it built thrust. These were among the largest aluminum forgings produced in the U.S. at the time, measuring long and weighing in at . The four stabilizing fins withstood a temperature of . The five F-1 engines were ignited in 3 staggered events, where the center engine was first ignited, followed by a diagonal pair of outer engines, and then the remaining two outer engines. These three ignition events were separated by just 300 milliseconds. This staggered ignition approach lessened the loads on the thrust structure, as an instantaneous ignition of all five engines would impart immense stress on the stage. Above the thrust structure was the fuel tank, containing of RP-1 fuel. The tank itself had a mass of over dry and could release .
Nitrogen was bubbled through the tank before launch to keep the fuel mixed. During the flight the fuel was pressurized using
helium, which was stored in tanks in the liquid oxygen tank above. Both the thrust structure and fuel tank had alternating black and white paint in order to monitor the vehicle's
roll during flight. Between the fuel and liquid oxygen tanks was the intertank. This contained propellant fill and drain lines for the liquid oxygen tank as well as a portion of the five liquid oxygen feed lines for the engines. The liquid oxygen (LOX) tank held . It raised special issues for the designer. The lines through which the LOX ran to the engine had to be straight (as any bend would slow the flow of LOX, which would necessitate even larger and heavier piping) and therefore had to pass through the fuel tank. This meant insulating these lines inside a tunnel to stop fuel freezing to the outside and also meant adding five extra holes in the top of the fuel tank. Atop the liquid oxygen tank sat the forward skirt, which connected the S-IC to the S-II stage and contained telemetry equipment and LOX tank vent lines. Two solid motor retrorockets were located inside each of the four conical engine fairings. At separation of the S-IC from the flight vehicle, the eight retrorockets fired, blowing off removable sections of the fairings forward of the fins, and backing the S-IC away from the flight vehicle as the engines on the S-II stage were ignited. The propellant tanks of the S-IC were manufactured from 2219-series aluminum panels, while the interstage, forward skirt, and thrust structure were built from 7075-series aluminum. The latter three sections also were corrugated with external stringers, providing additional structural support. The propellant tanks did not feature external stringers, as the tank pressurization provided sufficient rigidity. The S-IC also carried the
ODOP transponder to track the flight after takeoff. Image:SaturnV S-IC.jpg|Cutaway diagram of the S-IC. Image:apmisc-MSFC-6870792.jpg|Saturn V first stages S-1C-10, S-1C-11, and S-1C-9 at Michoud Assembly Facility. File:Apollo 11 first stage separation.jpg|Apollo 11 S-IC separation. ==Stages built==