Three years ago, the U.S. Navy SEALs were told that they were not going to get their six ASDS (Advanced Seal Delivery Systems). 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, But last November, the sole ASDS caught fire, and burned for six hours. The navy is reluctant to repair the vessel. Instead, another attempt is going to be made to develop a similar vessel, using components of the ASDS that did work.
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.