Introduction--------------------------------------------------------------
I have put some forethought into this, and I think it's time that Blockland had some sort of underwater-based vehicle.
It would be someone modeling a Submarine using Blender or other modeling program, to make a vehicle that would be spawned normally on the Vehicle Spawn in Blockland.Some pictures of submarines are shown here:

Shown above, is a U-Boat. Standard Armament: Torcreeps & Cannon/Machine-Gun

Shown Above, is a Nuclear Submarine. Hence their name, most of these vessels usually carried nuclear-based weapons on board.
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Function--------------------------------------------------------------
The submarine would be a medium-to-large sized vehicle that has some form of combat capabilities like the ability to shoot torcreeps.
I have also been toying around a bit with blender, and I think that that is basically what it would look like in real life.
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Movement and Diving--------------------------------------------------------------
Perhaps making the vehicle move in a similar manner to the box train, except it will turn faster.
As for the diving up/down;
I currently have two ideas for how to pull this off:
The Submarine could operate in a similar manner to the player's float/dive capability. You would hold shift to dive and release it to rise to the surface
-or-
The Submarine could operate in a similar manner to auto jet, the vehicle would have some form of keybind that you use to rise/fall in the water.
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Torcreeps & Other Combat--------------------------------------------------------------
If the submarine were to shoot torcreeps, I'd suggest that the torcreeps were only able to be armed underwater to help prevent people using them as missiles or other things like that.
The torcreep would have a propellor animation on the rear, it would make an ambient noise like propellor ambience or water displacement (sounds that water makes when objects pass through it) or something as it moves through the water
A particle emitter would be good too, like bubbles coming out the back of the torcreep as it moves.
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Other Armaments--------------------------------------------------------------
Other Armaments such as a roof-mounted machine gun or cannon such as the ones on U-Boat Vessels.
A model for the machine gun could be similar (but not limited to) the 'MG' Vehicle that is currently spawned on the vehicle spawn.
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End--------------------------------------------------------------
I hope that someone is able to make and script this, I do not have the skill nor the avaiable time to devote to such a project. But the idea is out there, and I hope that it will be discussed.
And as people have said time and time again, "If you dont care, dont post". If you just want to reply with negative comments then dont post at all. This is a discussion not a troll hive.