This really ought to be a very simple and straightforward question, but it's causing debate... If a Mech that mounts UMUs enters Depth 2+ water directly (via an external jump pack, drop parachute, pushed right off a cliff, etc.) does it sink to the bottom and make a PSR for entering water, or does it stay near the surface thanks to its UMU equipment, simply ending its movement?
The TacOps rules stated for the UMU itself (p295) seem to indicate that a PSR is required for entering Depth 1 water because walking movement was used and UMU MP expressly can't be used in Depth 1, but these rules never mention entering right into Depth 2+ water by other means.
In the rules for fighting aboard ships (p157 being the first page mentioning Mech UMUs) it mentions that UMU-equipped Mechs that fall off a large naval vessel are placed at Depth 2 (I think? The wording there is a bit fuzzy) and they take no falling damage and no additional PSRs.
The latter part indicates (well, former part, by page number) that stopping at Depth 2 is an automatic function of the UMU and doesn't require UMU MP to be spent, but that's never explicitly stated to be the case when non-UMU MP are deliberately spent to get there.