It would be quite difficult, first it should turn off the engines and cover the lids (particularly engine intakes and exhausts), or needs a snorkel (which we so far lack in the evidence).
Also the platform would require visibly huge stabilizers to move under the water, to conduct such a short maneuver right before arriving at the target, adjust its depth, maintain it (let's assume depth of target is known and fixed). Also would require rather complicated detection mechanisms for metallic objects above it, to detonate the warhead. Also further, it would loose the SATCOM / Starlink comms which needs to be autonomous from that point on.
Also the contact fuses suggest it is made to contact while sailing on surface.
Contact fuses is the key here, they should explain themselves how it works. I totally agree with this last point, you shoulnd't have them if your intention is to explode the charge underneath the ship.
My guessing for a hypothetical updated version would be a predicted action based on it's computer rather than a fully unmaned submarine device. How it should look like IMO?
Assuming the device contains a logic chip/CPU with it's embeded SO, you may create an algorithm which calculates the exact or approximate maneuver the USV should do to perform this action.
-Assuming that the USV has a relatively effective way by itself to estimate the range to the target (laser, cameras, gps?).
-Main variable would be the profile of the ship to attack, ( span and draft ?) it should be relatively easy to get that data and select it from remote.
-You can get location, speed and slope from your own sensors, so you can calculate the whole maneuver to be done, adjusted from previous tests.
So...
-You won't need huge stabilizers, although fixed fins are not seen on the pictures we have, it can be done with moving fins mixed with fixed ones deployed at the moment of the triggered action.
-About intake, should be good to go with an oxigen tank, as stated before. Exhaust, just as sailboats, wet exhausts. It just needs a few seconds to make the effect.
-Internal tanks to be filled, they could take advantage of internal water stream to the engine refrigeration system, for filling them up without needing any additional pump.
Then basically when you trigger the action of "armed" it should be smart enough to submerge 10-15 meters underneath the ship when it stimates it's near enough.
Additional technology could be only for deployed/fins and watertight internal gates. In my opinion completely feasible archievement.
.
Does anyone still have doubts why Ukraine needs reliable air defense systems?
