Dubbins presents a charming history of the WW2 Underwater Demolition Teams (UDT), framed around 95 year-old veteran diver George Mason. Mason was basically an average Depression era kid, but one of his high school jobs was as a lifeguard, which plucked him out of the standard Navy recruitment track and into the hazardous world of combat divers.
The job of the UDTs was to scout and clear beaches before amphibious invasions. Their equipment was primitive: a glass mask, rubber flippers, a knife, weighted lines for mapping, and explosive charges. Wetsuits were in the future, and scuba gear was novel technology abandoned after an early rig killed a diver.
Mason fought at Omaha Beach, Iwo Jima, and Okinawa. He never told anyone about what he experienced, and Dubbins was unwilling to badger details out of him, but the outlines are rough enough. Omaha Beach was a killing ground with thousands of casualties. At Iwo Jima, the divers went in first and drew a hail of heavy gunfire which disabled many of their support gunboats. The Japanese held their defensive fire at Okinawa, but months on the perimeter fending off kamikaze strikes was its own hell. UDTs were partnered, and Mason's partner David was killed in one of the final missions, leaving behind an infant daughter he never met.
Fortunately for this book, where Mason's individual memories fail, Dubbins can draw upon the broader UDT story and their renegade commander Draper Kauffman. Kauffman wanted nothing more than to follow his father as a destroyer captain, but was blocked from Annapolis by weak eyes. He joined the Navy Reserves, and then volunteered to serve as an ambulance driver in France in 1940, was captured and released, volunteered again as a bomb defusal technician for the British Navy, and spun up the UDT in the wake of fiasco at Tarawa, where the Marines were landed 500 yards offshore on a coral reef. Kauffman lead from the front, came up with the first "hell week" to separate out his recruits, and basically invented UDT doctrine on the fly.
I don't think this book treads a lot of new ground, but it explores a fascinating chapter in military history.