They were equipped only with swim fins, face mask and a slate board with a lead pencil on which to record intelligence gathered … their only weapon was a knife (thus, nearly defenseless or ‘naked;’) they were part of the Underwater Demolition Team (UDT.)
The Pacific Underwater Demolition Teams originated at Waimanalo Beach in December, 1943. (A ‘Naked Warrior’ monument commemorates their training at Bellows.)
On November 19, 1943, five thousand US Marines invaded Tarawa Island in the Gilbert Islands. Offshore coral reefs and other obstacles in the surf had resulted in many of the Marines drowning or being hit by enemy fire because their landing craft could not reach the beach.
Tarawa proved that troops should not be sent against enemy beaches until a thorough off-shore reconnaissance had been made.
To prevent a repetition of Tarawa it was necessary for trained personnel to search the water off the beaches and remove obstacles to make the passage from ship to shore nearly safe as possible. UDTs were organized in the Pacific following the Tarawa invasion.
UDT-1 and UDT-2 (each with about 15-officers and 150-enlisted men) were formed at Amphibious Training Base (ATB) Waimanalo, which was situated in proximity of today’s Bellows Air Force Station (AFS.) (By the end of the war, there were 34 UDTs.)
War planners realized success would require massive and numerous beach attacks from Africa to Normandy to hundreds of islands in the Pacific. Every one of those beaches was defended by an intricate network of underwater obstacles, booms, mines, chains and barriers.
Some were straight angled pillars and some were L-shaped, X-shaped and H-shaped “hedgehogs” that functioned even when knocked over. The obstacles could rip the bottom out of landing craft and often were topped by “teller” mines, flat plate-shaped explosives (“teller” is German for “plate.”)
Initially, about thirty officers and one-hundred and fifty men trained in underwater demolition work at Waimanalo. The original teams were comprised of men from the Navy, Army and Marine Corps.
After their first combat deployment in January-February 1944, UDT training was moved to Kihei, Maui, because Waimanalo didn’t have the space or facilities needed for demolition training.
The Naval Combat Demolition Training and Experimental Base, Maui was set up on the beach near the pier of the Kamaole Amphibious Training Base. (A monument commemorating UDT-14 is at Kamaole Beach Park I, in Kihei.)
Some of the first to go ashore in combat were 6-man units, called Navy Combat Demolition Units; divers located obstacles, mapped lines of attack, disarmed mines and demolished natural and man-made beach blockages.
During their early missions, Navy combat swimmers were completely clothed in combat uniforms, boots and metal helmets. That changed during a mission in preparation for the invasion of the Japanese held atoll of Kwajalein in January 1944.
Ordered to conduct a reconnaissance mission to assess beach conditions in advance of the planned assault, the two man team of Ensign Lewis F. Luehrs and Chief Petty Officer Bill Acheson could not get close enough to shore because of a coral reef.
They stripped to their underwear and swam over the reef to complete the mission undetected, becoming the first “Naked Warriors.”
Following the success of that mission, training emphasized strong swimming skills and operating without the use of lifelines, wearing only face masks, swim trunks and fins.
Underwater Demolition Teams were the foremost precursors of today’s Navy SEALs (starting on the windward coast of Oʻahu, in Waimanalo.)
The concept for development of an improved “Naval Guerrilla/Counter-guerrilla Warfare” capability within the US Navy was delineated in a March 10, 1961 Navy memorandum of recommendations.
Included was a recommendation for a wide range of “additional unconventional warfare capabilities within, or as an extension of our amphibious forces.”
The same memorandum stated that, “An appropriate name for such units could be ‘SEAL’ units, SEAL being a contraction of SEA, AIR, LAND, and thereby indicating an all-around, universal capability.” (Navy)
A bronze “Naked Warrior” statue greets visitors at the Navy UDT-SEAL Museum in Fort Pierce, Florida. (Lots of information here is from Navy and Navy UDT-SEAL Museum.)