Rest assured, SCRU is not name of the new roadhouse that’s opening up down the block, but would you believe that it’s a government agency and a venerable one at that? The Submerged Cultural Resources Unit was established in 1975 by the National Park Service to explore, survey and protect “historic shipwrecks and other sites important to American heritage.” Submerged (Newmarket Press, 275 pp, $25.95) chronicles the adventures and accomplishments of the historians, archeologists, photographers and extreme divers who made up that pioneering unit—but not the acronym, so they say.

Armed only with a degree in philosophy, author and SCRU leader, Daniel Lenihan, began his working life as a school teacher. He was also an passionate recreational diver, more specifically, a cave diver. (In later life, he describes the extreme sport as “dancing on the razor’s edge.”) With the faint hope that he might someday land a job that involved his avocation, he earned an advanced degree in anthropology at Florida State University, (cave diving between classes) and very shortly was hired as a “Park Ranger/Archeologist” by the National Park Service. It was the beginning of a career dream come true.

Lenihan’s first assignment was to assemble a team to undertake a shipwreck survey at Gulf Islands National Seashore (now Dry Tortugas National Park—accessible to the public via high-speed ferries from Key West). For the next 25 years Lenihan and his SCRU team performed similar functions in underwater park sites around the country and in both territorial and foreign waters.

In 1976, the team was training for a four year NPS project which focused on a study of the land inundated by the massive dams of the Southwest. In 1980 SCRU successfully located a treasure-laden Spanish galleon somewhere in or near Biscayne Bay. After a reconnaissance trip to Micronesia to investigate the feasibility of opening the waters to recreational diving on some of the sunken World War II vessels, the team was assigned to survey ten shipwrecks scattered around Isle Royale National Park in Lake Superior. Then on to Honolulu to dive on the USS Arizona—where they discovered live ordnance mere feet from the tourist walkway that comprises the above water monument. And then to the coast of France to investigate a civil war Confederate raider sunk off Cherbourg in 1864.

Hopping from one exciting underwater challenge to another right up until his retirement, Lenihan and his team have been the subject of many national TV specials produced by CBS, PBS, BBC, National Geographic and others. Submerged is a frank and personal look at those challenges from the inside—the out-takes, if you will. Lenihan’s easy conversational writing style belies the urgency of the most hair-raising risks and rescues, the most somber recoveries of the bodies of divers who didn’t make it.

Every water-oriented reader with the exception of members of the civilian shipwreck salvage community will be enthralled by Lenihan’s underwater world, the historical significance of many of the team’s investigations, and the derring-do of individual divers. The commercial salvors loudly deny that they are motivated by greed or reek havoc on historical sites that should belong to the American public. They call the SCRU team “bureaucrats” on the public dole, which makes the book highly controversial in some circles. All the more reason to read it.