If you are talking about single-stage-to-orbit (SSTO) submarines, I should tell you that the Sea Dragon is kind of like that. It is 75 feet in diameter, and pro

If you are talking about single-stage-to-orbit (SSTO) submarines, I should tell you that the Sea Dragon is kind of like that. It is 75 feet in diameter, and produced in an ordinary maritime shipyard out of steel. This is larger in diameter than any submarine ever made. The Russian Typhoon submarine class is 75 feet wide, but it is not round (it is shorter high than it is wide; flat top). http://en.wikipedia.org/wiki/Typhoon_class_submarine http://en.wikipedia.org/wiki/Typhoon_class_submarine A major difference between the Sea Dragon and an SSTO submarine would be the fact that a Sea Dragon is a staged vehicle. Only part of it would make it to orbit. It does launch from the sea, by the way. It could potentially be scaled up to whatever your preferable size is. Is there a particular reason why you would want a big metal submarine in orbit?