The Saturn V is arguably the most famous heavy lift rocket that the United States has constructed. That "V," though, implies that there were a few other rockets in the Saturn family before the fifth one showed up. This picture, from the historical archives of NASA's Marshall Space Flight Center, shows three Saturn I rockets under construction in Alabama.
The Saturn I was powered by a cluster of eight of Rockeydyne's H-1 engines, which were the final refinement of an engine design that started with Germany's V-2 rocket. These particular vehicles, the first stages for missions SA-4, SA-6, and SA-7, were intended for the final qualifying flights of the Saturn 1, before the rocket would be put into service lifting Apollo modules for orbital testing.
After the Saturn 1, NASA put together an "uprated" version, the Saturn IB, with a much more powerful second stage. The Saturn II was a concept for a "shorty" Saturn V, but it was never built, and neither was the Saturn III or IV, which were also intermediate designs. Instead, NASA ended up using the IB for Earth orbit payloads (like Skylab), and the Saturn V to get to the Moon. And now? We've got the Delta IV Heavy, but what we're really waiting for is SpaceX's Falcon Heavy, which is scheduled to have its first flight in 2015.
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