Artist concept of the Sea Dragon in the water. Aerojet via Astronautix.
Imagine standing among the small crowd in a viewing gallery aboard a command ship floating 35 miles off the coast of Cape Canaveral. Five miles away you see the upper portion of a rocket bobbing gently, waves lapping at the fuselage. Though isolated at sea there’s a buzz of activity in the air. The conversation on board is punctuated by a loudspeaker booming status updates on the rocket in the water. Finally, an announcement crackles saying that the Cape has given a GO for launch. With NASA’s blessing, the launch director on board begins the final countdown. You hear a distant rumble as a massive engine roars to life under water and gets progressively louder as the rocket starts to rise. In just seconds the staggering, 400-foot behemoth leaves the ocean and disappears from view into the sky. In less than a half hour its 1.1 million pound payload will be in orbit around the Earth.
This was the future Aerojet foresaw with its 1963 proposal for the Sea Dragon rocket.
John Glenn's launch on an Atlas in 1962. NASA.