Smithsonianmag.com offers an excerpt from Andrew Dubbins’ Into Enemy Waters: A World War II Story of the Demolition Divers Who Became the Navy SEALs.
In the 1940s, most of the Pacific Ocean’s enormous underwater realm remained uncharted. Instruments and equipment were too rudimentary, the ocean too vast and much of the sea bottom too difficult to reach. Nautical charts showed the location of Pacific islands and atolls but offered little detail about the depths or underwater features of their beach approaches. Advances in sonar allowed United States ships to measure the ocean floor in deep water but not in the shallows surrounding land masses.
With no charts or technology available to guide vessels onto enemy shores, the job fell to the roughly 1,000 young swim scouts of the U.S. Navy’s Underwater Demolition Teams (UDT), who were assigned to reconnoiter enemy beaches and clear coastal defenses ahead of Allied landings during World War II. These so-called frogmen swam into beaches unarmed, wearing only swim trunks, dive masks and fins.
You can read the rest of the piece via the below link:
You can also read my Counterterrorism magazine piece on the UDT and Navy SEALs, which featured my later father, former UDT 5 Chief Edward M. Davis (seen in the center of the above Photo), via the below link: