A year ago, the U.S. Navy cancelled its ASDS (Advanced Seal Delivery Systems) minisub project, after over a decade of effort, and nearly a billion dollars spent. This inspired a commercial submarine company (Submergence Group) to try and build what the SEALs needed, but do it more quickly and cheaply. So, in less than a year, and spending about $10 million of their own money, Submergence Group delivered their S301 SEAL delivery system minisub to the navy for evaluation. The S302 was built to commercial standards. It can dive to 200 meters (600 feet) and has an air locks so that divers can enter or leave the S301 while submerged. The 13 ton, 8 meter (25 foot) S301 carries two crew and eight SEAL commandos. The S301 can fit into the 12 meter (38 foot) dry deck shelter that can be attached to American SSNs. This allows the S301 crew and passengers to enter the minisub via a SSN hatch. Then the dry deck shelter is flooded, and the S301 can proceed to the target area. The S301 provides 12 hours of operation via lithium ion batteries. The navy was so impressed with the S301, that they leased it for a year, to see if it, or a variant, could meet the ASDS requirements. All this was made possible by the fact that commercial materials and shipbuilding technology had advanced so much in the last two decades, that a recreational submarine industry had developed. These private subs are not cheap, but for the very wealthy, and maritime research operations, they are affordable.
It was four years ago that the U.S. Navy SEALs were told that they were not going to get their six ASDS. Only the first one had been built, and it was not a success. After a decade of development, the ASDS had too many technical problems, and construction of the other five was cancelled. Only the first one remained, and it sort of worked. Then, fifteen months ago, the sole ASDS caught fire, and burned for six hours. The navy was reluctant to repair the vessel. Instead, it was decided to try and develop a similar vessel, using components of the ASDS that did work. In the meantime, the S301 showed up, rather unexpectedly.
The ASDS was a 65 foot long, 60 ton mini-submarine. Battery powered and with a crew of two, the ASDS could carry up to 14 passengers (fewer if a lot of equipment is being brought along, the usual number of passengers is expected to be eight.) With a max range of 200 kilometers, top speed of 14 kilometers an hour and max diving depth of 200 feet, the ASDS operates from one of the seven nuclear submarine equipped to carry it on its deck. The ASDS is equipped with passive and active SONAR, radar and an electronic periscope (that uses a video camera, not the traditional optics.)
While a nice piece of engineering, each ASDS cost over $300 million. Fortunately for the navy, SOCOM (Special Operations Command) was paying for the ASDS boats. That means that army rangers and marine recon troops would also train to use ASDS. Delta Force was to try them out as well. Little is said publicly about how often, and where, ASDS would be used. The types of missions ASDS was designed for are often kept secret for a long time.
The ASDS first production boat underwent testing in Hawaii and the Persian Gulf for three years, before being declared ready for service and in 2004. But problems kept cropping up, until the production of the other five was cancelled in 2006. Apparently there was not a big demand for something like the ASDS, as there was no urgent request for a replacement design.
The S301 saves a lot of money by skipping lots of the high tech sensors, and "additional features" that some admiral or contractor tacked on for no particular reason (but that increased the cost, and complexity, of the system a lot.) The regular warship builders and defense contractors dismiss something like the S301 as a "civilian toy," but the troops have some input, and they are definitely interested.