you could spare all your confusion by RTFM
...i know, many mods, many manuals... but my is one of those who are worth reading it
...but also the F1 help screen tell you that this keys have changed for toggeling rise/lower the periscopes while playing a sound which is hearable while in 3d space.
...but i know that the current SDBSM keys for operating the hydrophone are a bit "unlucky"
another thing, dont try to move the hydro using the mouse wheel, it plays the periscope zoom motor sound.
while using SDBSM the hydrophone is operated using SHIFT+HOME and SHIFT+END keys.
the readme also explain how to change or customize your keyb. layout.
...hope that helps