onlywaterweapon=true,

[Forboding Angel]

Needed. We have weapons that work only outside of water, weapons that work outside and inside water, but the only weapon that only works in water, is the torpedo weapontype.

[Anarchid]

Would that mean that the weapon can shoot only when submerged, or that it can only shoot submerged targets?

[Jools]

No. Torpedoes can also hit ships, and should also be able to hit hovercraft.

It should work so that it can hit things that are in water or close to it. Actually, ships are submerged, that's where the torpedo hits. But I don't think the engine sees ships that way.

[Forboding Angel]

The weapon would only be able to fire when submerged.

For example, a torp can be force fired from out of water, but it does not gain any velocity.

In this case, the other types of weapons, like lasers, missiles, cannons, etc could only be fired when underwater.

Of course, lasercannons would probably be the most useful weapontype used with this tag, but the others leave you free to use your imagination.