The Stealth Swimmers Whose WWII Scouting Laid the Groundwork for 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. Training was conducted at the UDT’s Maui base, a facility consisting of basic tents, a ramshackle mess hall, cold open-air showers and smelly outdoor toilets.