A group of officers and enlisted specially trained and equipped for making hydrographic reconnaissance of approaches to prospective landing beaches; for effecting demolition of obstacles and clearing mines in certain areas; locating, improving, and marking of useable channels; channel and harbor clearance; acquisition of pertinent data during pre-assault operations, including military information; observing the hinterland to gain information useful to the landing force; and for performing miscellaneous underwater and surface tasks within their capabilities.