This question is closely tied to Feign's question posted here
http://bg.battletech.com/forums/index.php?topic=56464.0, and the answers to it, or even the very validity of this question may depend on answers to that question (which I feel has not been fully answered yet - the current answer does not cover the case of 'Mech falling from a cliff into water for example).
The short version of my question is - what damage an UMU-equipped unit takes if it falls from above unit surface into water hex? Rules on p. 57 TW say that a unit falling from above surface into water hex takes damage twice - once for hitting the water surface, and the second time for hitting the bottom. The answer to Feign's question seem to suggest, that at least in case of an UMU-equipped 'Mech falling from a large naval vessel into Depth 2+ water it does not hit the bottom (and therefore should not take damage for hitting it), but what about:
1. UMU-equipped 'Mechs or other units falling from somewhere else than large naval vessel into water hex (Depth 2+ water for 'Mechs - see p. 295 TO, Depth 1+ for other units)? Do they hit the bottom, and take normal damage? If they don't hit the bottom at what Depth/Elevation do they end up? This question seems valid even if a unit begins it's fall bellow the surface - like when falling from a deck of a submerged submarine, or being pushed from a bottom of a water hex to a deeper water hex?
2. What about a unit at the bottom falling into a swallower hex (after a push - p.147 TW/charge - p. 148 TW/domino effect - p. 152 TW for example), a hex with the same depth, or just the same hex (same situations as before plus kicks p. 147 TW, failed PSRs for entering a water hex if a 'Mech is walking, or falls resulting from taken damage)? I would assume, that UMUs don't help in those such cases. Is that correct?
3. What about a UMU-equipped 'Mech in water, but not standing at the bottom? Can it even fall as a result of damage taken, physical attack or domino effect? What if a physical attack or domino effect moves such 'Mech into a swallower hex, then 'Mechs current depth?
4. What about damage for hitting the surface? If a unit falls from a hex or a deck of a large naval vessel, that is above water into water hex, I would assume, that UMUs don't protect from damage from hitting the water surface regardless of whether the water is deep enough for the unit to use UMUs in it or not.