Callisto
From Acw
Callisto is a moon of the planet Jupiter. Outermost of the 4 Galilean moons (those discovered by Galileo Galilei), it is the second largest of Jupiter's moons, making it the third largest moon in the Sol system.
Callisto was considered unsuitable for anything but resupplying chemically propelled craft on their way to the Saturn sub-system, until 2347, with the construction of the first French extraterrestial colony of Cousteau - at a depth of 5,600 feet below sea-level.
Cousteau
Cousteau, named after Jacques Cousteau, the explorer, politician and initiator of France's long-standing Programme Pelagique(Deep-sea program) in the second half of the 20th century, is the long-awaited first step in France's interstellar ambitions. While a remarkable engineering feat, it is perhaps an overdue development, given the length of time humanity has been in space, and the increasing viability of underwater cities on Earth itself - an advance largely driven by French science.
Due to the customary secrecy surrounding the Programme Pelagique, little is known of Cousteau's size, design, population or produce, beyond the obvious scientific research and national pride.
France claims Callisto
As of 2360, France has claimed sovereignty over the entirety of Callisto's oceans, citing sole settlement of the planet's unbroken undersea landmass - and it looks likely to be granted this concession by treaty, if it bows to US and Nazi demands to allow unrestricted refuelling from the planet's seas.