In 1998, salvager Paul Tidwell and his company Cape Verde Explorations led an expedition to the wreck site of the World War 2 Japanese cargo submarine I-52 in the mid-Atlantic. Resting at a depth of 5240 meters, it had been located and then identified using side scan sonar and an underwater tow sled in 1995. War-time records indicated the I-52 was bound for Germany, with a cargo including 146 gold bars in 49 metal boxes. This time, Mr. Tidwell's company had hired the Russian oceanographic vessel, the "Akademik Mstislav Keldysh" with its two manned deep-ocean submersibles "MIR-1" and "MIR-2" (figure 3). In order to facilitate precise navigation across the debris field and assure a thorough search, "MIR-1" deployed a long baseline transponder network on the first dive. Over a series of seven dives by each submersible, the debris field was progressively searched. The LBL positioning record indicated the broadening search coverage after each dive, allowing the team to concentrate on yet unsearched areas during the following dive. No gold was found, but the positioning system had documented the extent of the search. In recent years, several trends in underwater acoustic positioning have emerged. One is the introduction of compound systems such the combination of LBL and USBL in a so-called LUSBL configuration to enhance performance. These systems are generally used in the offshore oil & gas sector and other high-end applications. Another trend is the introduction of compact, task optimized systems for a variety of specialized purposes. For example, the California Department of Fish and Game commissioned a system (figure 4), which continually measures the opening area and geometry of a fish sampling net during a trawl. That information helps the department improve the accuracy of their fish stock assessments in the Sacramento River Delta.