This look like a terrible idea, it has the worst of both surface ship and subs.
It's probably as slow as a sub, but since it cannot submerge fully, it will be as detectable as surface ship, not to mention it lacks all sensors associated as surface ship, so it has to operate with other surface ships in groups, so that means it became target.
Why not just make an surface arsenal ship, or a pure VLS nuclear sub?
I don't think the second paragraph is necessarily true.
First of all, being able to semi submerge with only its conning tower/s surfaced, its radar cross section would be significantly smaller than a comparably sized surface ship with a similar number of VLS, unless you expend substantial funds on trying to reduce the RCS of a large surface ship, and the end result will probably still have a larger RCS than a semi submerged ship with only its conning towers exposed.
The purpose would not be to make the semi submersible ship have zero surface RCS, but rather to have a cost effective way of significantly reducing its surface RCS, by submerging most of the ship under the waves, instead of a conventional ship where most of it is above the waves at the waterline and forced to use extensive RCS reduction measures to make it a little more survivable.
As for lacking sensors of a surface ships -- that is a fairly standard idea for arsenal ships. Arsenal ships are not meant to be multi purpose ships with capable sensors, they're meant to be ships that have a lot of missile tubes and get the vast majority of their targeting data from other sources, and in a high intensity warfare situation will likely operate as part of a larger task force.
I think such a ship would not be intended to operate alone and stealthy against a high capability foe, but instead would operate as part of a larger task force against a high capability foe, and its RCS reduction measure/semi submersible nature is meant to make it a smaller target that's harder to accurately track/id/engage
within that task force. Arsenal ships are generally not thought of as multipurpose surface combatants with their own high capability organic sensors, but rather as minimally crewed self propelled missile barges.
This
, I think gives a good rundown of the basic hallmarks of an arsenal ship.
Interestingly, the author says it would be of interest to reduce such a ship's RCS, and says "A long series of VLSs encased in a largely submerged hull would be optimal" as well as: "the ship’s freeboard should be as low as possible and not have a substantial superstructure—think of an iceberg with its top flattened. The most efficient method of doing this is by having the capability of ballasting down, similar to that of amphibious warships. With ballast tanks, voids, and fuel tanks along its underwater hull, and an internal double hull, a modicum of protection might be achieved against torpedoes and mines." The author envisions a mostly conventional hull surface ship with low freeboard that can be achieved by ballasts.... BUT, of course a natural but more extreme extension of this idea, is to have a semi submersible hull, which leaves only the conning towers exposed on the top, to further reduce RCS.
as for why not a pure VLS nuclear submarine -- a SSGN fills a different role to an arsenal ship, as it is a much more stealthy and much more capable but also much more expensive vessel that would likely operate alone rather than as within a task force when fighting against a high capability foe. I'm sure China is interested in SSGNs, but those construction slots at this stage are probably better used for building real SSNs and SSBNs first, or at least to give a few SLCM VLSes for their SSN classes.
Again, I'd like to emphasize I don't necessarily believe this project is definitely real, but I think there are enough indications to warrant discussion over the rationale and purpose of such a ship if it turns out to be real.
