With a diameter of 75 feet (23 m) and a projected height of a staggering 490 feet (150 m), and weighing in at just under 40 million lb (18,143 tons), Sea Dragon was designed like a freight train ...

"The Sea Dragon concept has been developed assuming that space transportation economy will result if launch vehicles are used that are very large, simple, and reusable, even if payload-to-liftoff ...

The Sea Dragon, a declassified 1960s project, was a massive 500-foot-tall rocket designed to launch from the ocean, carrying huge payloads into space at a fraction of the cost.