The player will control his air and naval forces in real time on the Globe.
Did you say naval forces?? There weren´t any naval forces in the previous UFO: Extraterrestrials nor in the original XCOM:UFO Defense. Why did you decide to implement the navy in the "UFO2Extraterrestrials: Battle for Mercury"?
That´s because the aliens have not limited their activity to land. They are also terrorizing the seas and oceans. They have been abducting people from their civilian vessels (yachts, boats, tankers, and cruisers). So the CAF have begun utilizing aircraft carriers to protect the oceans of Earth even as the bases protect the land.
Actually, the aircraft carriers in "UFO2Extraterrestrials: Battle for Mercury" won´t be aircraft carriers per se, but a kind of heavy aircraft-carrying assault cruisers with a VTOL system and they will be armed with missiles and other defenses against numerous disc shaped enemies. These defenses will help protect the cruiser. However the main weapon will still be your Fighters. Maintaining fighters on your aircraft carriers will enable them to reach any endangered civilian ships that much faster.
The missions will take place not only in cities, forests, deserts, bases, etc., but also on boats and the Aircraft Carriers.