LJK said:

"The Gemini missions of 1965-1966 were key to the success of Apollo. Mercury just did not do enough for all that the astronauts needed to make a Moon landing a success."

This is completely true. Gemini established the technology of manned orbital rendevous and EVAs. Basic technologies like fuel cells, space based radar and on-orbit repair were also demonstrated by Gemini.

However a big driver behind Gemini was the militarization of space. Gemini went into orbit on a Titan-II ICBM. The Titan II had to be man rated because of Gemini (there were significant pogo problems with the earlier verions of the Titan-II that made man rating it difficult). The Titan-II was the core technology for the Titan-III. The Titan-III was intended as the launch system for the Manned Orbital Laboratory (MOL). The MOL was essentially a man tended spy satellite. The MOL was designed to use a Gemini spacecraft as its crew return capsule. The advent of CCD technology made the MOL unnecessary (Your digital camera along with your teflon cooking pan and RTV silicone adhesives are the results of Cold War aerospace military technology). Also there was another military program called the X-20, Dynasoar. The X-20 was designed to be launched into space on a Titan-II and function as a Low Earth Orbit (LEO) fighter plane. The Gemini spacecraft was essentially a capsule prototype for the X-20. Like MOL, the X-20 was cancelled before being deployed. I've been told that there were fundamental design problems with launching a lifting vehicle like the X-20 on the end a launch vehicle like the Titan-II.

America toyed with the notion of having a full blown "Space Force" in the 1960s but couldn't put the pieces together. Gemini was a biproduct that was useful for Apollo and NASA.

Gary