nuclear-capable underwater drone called Ocean Multipurpose System Status-6.
Forbes has a short article about anticipated advancements in the global submarine fleets. Technology is improving. More nations are starting to export submarines. Nations that have never had submarines before are putting them into service.
Perhaps most ominously a range of autonomous underwater vehicles with offensive capabilities are entering service. They range from torpedoes with artificial intelligence or mines that position themselves to a predetermined location, to an entirely new class of intercontinental range, nuclear powered, nuclear armed drones. In effect these include underwater cruise missiles. Since nations have seen fit to share cruise missiles with terrorist organizations, there is no reason not to expect that they will also share at least some of these weapons.
Chuck Hill's CG Blog 
Very telling…
I wonder if BRAC Base Closures will come back and haunt the USA in the future. Some port cities have nothing but the USCG as their defensive measures, nothing but guns and Phalanx CIWS as their main local defense. Gone are the Harpoon SSMs, torpedo tubes, and ASW helicopters. Some states have Air National Guard fighters, but they’re not ASW equipped.
The need for some class of corvette or LCS armed with OTH SSMs, sonar, and torpedo tubes gains monumental importance for CONUS defense.
Underwater Unmanned Vehicles (UUV) are unarmed for now…and that is the problem. UUVs can observe, but there’s nothing they can do to prosecute or protect unless they want to play Kamikaze.
Coastal ASW defense is left to the USN (wrangled from the USCG) and one would assume USN submarines are lurking in USA coastal waters for protection—assume, that is.
I am glad we Brits are preserving and building upon our submarine legacy to do our part to plugging the submarine gap facing us. And not doing something stupid like building aircraft carriers and buying expensive jets…………….Um………..Wait a cotton picking moment…….