posted 10-31-2008 03:29 AM
Just to amplify on others' replies, I'll summarize what I've learned about this topic from reading "Stages to Saturn," available on-line from the NASA history website.
Quite a number of Saturn stage configurations were considered between 1958 and 1960. One early version was the Saturn A-1, which had the familiar S-I stage plus a Titan I 1st stage as a 2nd stage and a Centaur as a 3rd stage. The Saturn A-2 was the same except that the 2nd stage consisted of a cluster of 4 Jupiters rather than a Titan 1st stage.
In the Saturn B-1, the 2nd stage was a custom-developed lox/RP-1 stage powered by 4 H-1 engines. Again, the Centaur was to be the 3rd stage.
Then there was the C-1: S-I plus S-IV plus Centaur, known in this application as the S-V. This is the Saturn I which actually flew, except that the S-V stage was never live.
The original C-2 design would have been S-I plus S-III plus S-IV plus, for some missions, S-V. The S-III was to have been a lox-hydrogen stage powered by two J-2 engines.
The original C-3 configuration was S-I plus S-II plus S-III plus, for some missions, the S-IV and even S-V. The S-II was to have had four J-2 engines and the S-I would have been upgraded either by increasing the thrust of its eight H-1 engines to 250,000 lb or by replacing the center four H-1 engines with a single F-1.
In December 1959, the Silverstein committee (formally known as the "Saturn Vehicle Evaluation Committee" or something like that) decided to skip development of the Saturn A and B configurations and go straight to the C configurations, which gave the most lifting power.
NASA HQ accepted the recommendations of the Committee and forwarded them to Hunstville. Huntsville concurred, but dropped the S-III stage. In the C-2 it was replaced by the S-II stage, with 4 J-2 engines. The upgraded S-I in the C-3 was replaced by a new stage powered by two F-1s. Eventually, as we all know, the C-2 and C-3 were dropped entirely. The C-4 was briefly considered (4xF-1 plus 4xJ-2 plus 1xJ-2) before being replaced by the C-5. The S-II designation was now applied to the 2nd stage of the C-5, of course.
Last night on YouTube, I found a NASA film about Saturn from the early 60s. I think it's a great shame that in the rush to get to the moon the C-2 was never developed. A manned lunar voyage using five or six C-2 launches would have been possible (see the extensive documentation available on the Army's Project Horizon that is available from astronautix.com), and the C-2 was small enough so that, unlike the Saturn V, it might have been feasible to keep it in production after the moon race had been won.