I have found something I want to work into the Cosmic Era setting, but I need some assistance.
The Ark ships from the disaster porn movie 2012 are pretty cool. Massive, self contained vehicles, superficially looking like spaceships, but actually ocean going, probably nuclear powered, or alternately powered.
When would these have been built?
The technology would be contemporary to the construction of the first generation arcologies, but predating the flying warships and spaceships. These could have been introduced at any point after the Resource Wars and into the Second Renaissance, functioning as oceanic arcologies, predating or being contemporary to raft cities, seacologies, etc.
Who would have built them?
The Chinese, Russians, EuroUnion, America, Japan? The new world powers, Atlantic Federation, ACPS, the Pacific Rim Coalition.
mobile cities, mobile sea bases larger than carriers to deploy mecha and armed forces, mobile factory ships to build seacologies, mobile research centers that are easier to maintain and crew than space operations.