The first stage of the Apollo Project's Saturn V launch vehicle.

In the early design studies, this stage was designed to use four rocket engines. However, before the development and construction contract was awarded to Boeing in December of 1961, it was recommended that a fifth engine be added in the center of the crossed beams that were to support the other engines. This change gave the Saturn V the increased capacity required for the later Apollo missions, which performed the lion's share of the manned scientific exploration of the moon.

The S-IC was designed 'within the state of the art', as it was felt, correctly as it turned out, that the sheer size of the stage would introduce enough headaches as it was. This value of the approach was seen, for example, with regard to the engine cross beams; as the beams were conservatively chosen to be much stronger than initially needed, they were able to support the proposed fifth engine with only minor changes to the S-IC's design. The engines chosen were F-1s, which had already been in development for a number of years, in anticipation of just such a booster as the S-IC.

The propellants chosen were a kerosene based fuel called RP-1 and liquid oxygen. RP-1 was chosen over liquid hydrogen (which was used in the S-II and S-IVB upper stages) both because of the easier engineering involved and because a larger (and so heavier) tank would have been required to hold all the liquid hydrogen needed to fulfil the S-IC's role. Use of the high density RP-1 also meant that two seperate tanks could be used to store the RP-1 and the liquid oxygen, avoiding the problems associated with a common bulkhead that plauged the S-II stage.

Wernher von Braun's team at Marshall Space Flight Center (MSFC) worked closely with Boeing, more closely than most contractors were used to working with their government contractees. However, MSFC's expertise proved invaluable in getting the booster from the drawing board to the pad.

Unlike previous boosters, the S-IC was assembled vertically, not horizontally, to prevent gravity distorting the frame under its own weight. As well as the new assembly facilities required for this, new techniques had to be developed to weld the lenghty continous joins of the stage. Huge stands were built to test it at MSFC and the Mississippi Test Facility, which performed the bulk of the static testing.

The S-IC can be broken down into three layers:

At the bottom, the first layer was the thrust structure which contained the F-1 engine assemblies and also contained four huge anchors which held the Saturn V in place on the launch pad and briefly after engine ignition to allow thrust to build up. The Saturn V's distinctive engine fairings and fins around the base were made from titanium. Each fairing also contained a pair of retrorockets that fired when the stage was discarded in flight.

Above the thrust structure was the RP-1 tank. When filled, it contained over 730,000 liters of fuel. The RP-1 was continously stirred prior to launch by bubbling nitrogen through the tank via the feed lines. In flight, the tank was pressurized by liquid helium stored in bottles located in the liquid oxygen tank above. The RP-1 was funneled to the engines at a rate of 4,900 liters per second.

The third layer consisted of the liquid oxygen tank and the forward skirt which connected the S-IC to the rest of the Saturn V. The tank contained 1,204,000 liters of liquid oxygen and used five suction lines which passed through the RP-1 tank and fed the oxidiser to the engines at a rate of 7,300 liters per second.

The S-IC stage first flew as part of an unmanned test of the Saturn V on November 9, 1967. Its last flight was as part of the modified Saturn V that orbited Skylab on May 14, 1973.

The S-IC was 10 meters in diameter and 42 meters high. It produced 33 million newtons of thrust for 170 seconds.