DARPA "Manta Ray" uncrewed underwater vehicle (UUV) testing in California.

For sure, and these companies love to make big ass expensive projects.

But realistically, a passive sensing buoy that costs 1/10,000th the cost is going to be able to 80% of the job. Hydrophones can be made tiny and the main reason submarines are big is because, well, people and the associated support systems. Not to mention almost all the actual work submarines are doing currently is passive.

Take for example the situation in Ukraine. I'm not saying there isn't a role for hundred million dollar predator drones, but whats really moving the needle are cheap, basically disposable (or like, quite literally disposable) multi-use, single munition drones. Why use big money boom boom when small money boom boom do job? Like you aren't launching a mark II from something the size of a beach ball, but you can have it sitting there listening and maybe scanning r/g/NIR lidar, sitting on 40kgs of C4, just waiting for a signal. It could be phoning home giving you a full 3d view of the local environment, and you and I could probably hack together a prototype in a few months. And for the price you can have 10k of these for every one of the big manta ray looking thing.

I want to see underneath it. I bet they are running red/green lidar.

it also seems to not realy go fully underwater. the fin is propably for the antennas