why not something like this?
Facts:
- I cannot imagine anything that goes under water 4800 knots without making huge tsunami wave.
- Also movement underwater is very similar to movement in low gravity enviroment like on moon / mars.
Interception:
- all interception is done in the air due to facts above
- if alien sub is UFO then after crash it can be taken by transport ship overland
- if alien sub is USO then after crash it can be taken by transport ship underwater but only shallow one (see Craft section)
- speed under water is very limited and basically its just craft moving to location and then wait to dive until specific location is reached
- UFO or USO type does not matter, actually alien race matters is this UFO or USO type (check Alien race section)
Alien races:
- there are space and water races
- space race does not live underwater (no crash missions)
- water race does not live over land (or some of them does not)
- water race shows up after 3-6 months
- based on race type, crash mission are available on land or / and water
Crafts:
- there is one transporter that is cappable of land and water mission
- skyranger can only take shallow water mission
- lighting can take shallow and medium water mission
- avenger can take any type of water mission (including final Tleth underwater) -> that is logical from story point of view
Types of missions:
- land mission done same as in x-com
- shallow water which is same as day mission on land (its day or night, 10% of all water)
- medium water which is same as night mission on land (its always dark, 20% of all water)
- deep water which cannot be accessed by x-com, all USO cannot be access there (70% of all water)
- so its all about setuping proper regions on the globe
Countries:
- existing countries should have more areas over seas
- few countries might be added to control more shallow seas areas like Indonesia / Arabia / Mexico
Weapons:
- standard, those that works only on land, cheap
- advanced, those that works on land on over water, more expensive
- balistics, land only
- laser, land only
- gauss which is laser that works underwater and land
- plasma, land only
- sonic which is plasma that works underwater and land
- distruptor / fusion works underwater and land
Story:
- starts as ufo 1, but ends as ufo 2 (cydonia underwater)
- there is one research tree but some technology from ufo 2 is moved to ufo 1 to
- most of battles are done over land, but some of them including the final one is done underwater
- as time passes the more and more battles are thought underwater, but still this is about 25% max
Alien bases:
- land aliens have bases over land
- water aliens have based under water but only in regions with shallow / medium waters, those can be accessed by x-com
- deep water cannot be accessed neither by aliens or humans but this is place of final mission
Terror missions:
- as only crashlands are done underwater then no terror missions are done underwater
- urban is used for inland cities
- port is used on coastal cities
- ship ?? i have no idea how to implement a ship
Tom