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Underwater Demolition Teams
Underwater Demolition Teams shoulder sleeve patch.JPG
Patch of the Underwater Demolition Teams from 1955 onward.
Active 15 August 1942 – 1 January 1983
Country United States
Branch United States Navy
Type Amphibious warfare
Role Underwater demolition, reconnaissance, seaborne infiltration and exfiltration
Garrison/HQ Fort Pierce, Florida, U.S.
Maui, Hawaii, U.S.
Nickname(s) UDT
Engagements Operation Overlord
Korean War
Battle of Iwo Jima
Battle of Okinawa
Operation Torch
Borneo campaign (1945)
Battle of Peleliu
Battle of Saipan
Battle of Tinian
Battle of Guam
Battle of Leyte
Invasion of Lingayen Gulf

The Underwater Demolition Teams (UDT) were an elite special-purpose force established by the United States Navy during World War II. They also served during the Korean War and the Vietnam War. Their primary function was to reconnoiter and destroy enemy defensive obstacles on beaches prior to amphibious landings. They also were the frogmen who retrieved astronauts after splashdown in the Mercury through Apollo manned space flight programs.[1]

The UDTs reconnoitered beaches and the waters just offshore, locating reefs, rocks, and shoals that would interfere with landing craft. They also used explosives to demolish underwater obstacles planted by the enemy. As the U.S. Navy's elite combat swimmers, they were employed to breach the cables and nets protecting enemy harbors, plant limpet mines on enemy ships, and locate and mark mines for clearing by minesweepers. They also conducted river surveys and foreign military training.

The UDTs pioneered combat swimming, closed-circuit diving, underwater demolitions, and midget submarine (dry and wet submersible) operations. They were the precursor to the present-day United States Navy SEALs.[2]

In 1983, after additional SEAL training, the UDTs were re-designated as SEAL Teams or Swimmer Delivery Vehicle Teams (SDVTs). SDVTs have since been re-designated SEAL Delivery Vehicle Teams.[3]

Early history

The United States Navy studied the problems encountered by the disastrous Allied amphibious landings during the Gallipoli Campaign of World War I. This contributed to the development and experimentation of new landing techniques in the mid-1930s. In August 1941, landing trials were performed and one hazardous operation led Second Lieutenant Lloyd E. Peddicord to be assigned the task of analyzing the need for a Human intelligence (HUMINT) capability.[2]

When the U.S. entered World War II, The USN realized that in order to strike at the Axis powers the U.S. forces would need to perform a large number of amphibious attacks. The Navy decided that men would have to go in to reconnoiter the landing beaches, locate obstacles and defenses, as well as guide the landing forces ashore. In August 1942, Peddicord set up a recon school for his new unit, Navy Scouts and Army Raiders, at the amphibious training base at Little Creek, Virginia.[2] In 1943, the Army and Navy jointly established the Scout and Raider School (Joint) at Fort Pierce, Florida. Pressure to further implement Human Intelligence gathering prior to landings heightened after Marine Corps landing craft were damaged by coral reefs during the Battle of Tarawa in November 1943. Aerial reconnaissance incorrectly showed the reefs were submerged deep enough to allow the landing craft to float over. Marines were forced to abandon their craft in chest deep water a thousand yards from shore, helping Japanese gunners inflict heavy U.S. casualties.[2] After that experience, Admiral Kelley Turner, Commander of the 5th Amphibious Force, directed that 30 officers and 150 enlisted men be moved to Waimanalo ATB (on the “big island” of Hawaii) to form the nucleus of a reconnaissance and demolition training program. It is here that the UDTs of the Pacific were born.[4]

In 1944 at the urging of Admiral Ernest King, the Army Engineers relinquished demolition jobs of obstacles in the surf zone and underwater to the U.S. Navy.The Army retained responsibility to clear any obstacles inland, although for Operation Neptune the Engineers and Navy demolition men worked cooperatively.[citation needed]

A memorial to the founding of the UDT is being built Bellows Air Force Station near the original Amphibious Training Base (ATB) Waimanalo.[5]

Naval Combat Demolition Units

It became apparent that in addition to the Scouts and Raiders, a group of specialists to destroy obstacles was required. In late 1942, a group of Navy salvage personnel received a one-week concentrated course on demolitions, explosive cable cutting and commando raiding techniques. The Navy Scouts and Raiders unit was first employed in Operation Torch, the invasion of North Africa in November 1942.[6] During Torch, this unit cut the cable and net barrier across a river in North Africa, allowing Rangers to land upstream and capture an airfield.

The NCDU members, each consisting of one officer and five ratings were to clear the beaches of obstacles for the invasion force with the team coming ashore in an LCRS inflatable boat with their explosives.[7]

Naval Demolition Units landed as part of the Allied invasion of Sicily; they were divided in three groups that landed on the beaches near Licata, Gela and Scoglitti.[8]

Having been inaugurated at Solomons Maryland, under the command of Cdr. John C. Daniel, the Navy's Demolition Units were to be expanded pursuant to Daniel's recommendations to move the training to Ft. Pierce, Florida. In 1943, the Navy decided to create a large dedicated force for such tasks: the Naval Combat Demolition Units (NCDU). On May 7, Admiral King, the CNO, picked Lieutenant Draper L. Kauffman USNR to lead the training.

The expansion of the force meant recruitment beyond the pool of experienced combat swimmers. Most of demolition volunteers came from the Seabees (the Navy's Construction Battalions). Training commenced with one grueling week designed to "separate the men from the boys". Some said that "the men had sense enough to quit, and left the boys." By the spring of 1944 this intense week was known as "Hell Week."

Kauffman's experience was at disarming explosives; now he and his teams were learning to use them offensively. One innovation was to use 2.5-pound (1.1 kg) packs of tetryl placed into rubber tubes, thus making 20-pound (9.1 kg) lengths of explosive tubing that could be twisted around obstacles for demolition.[9]

At the beginning of November 1943, six men from Kauffman's Naval Combat Demolition Unit Eleven (NCDU-11) were sent to England to start preparations for the Normandy invasion.Later NCDU-11 was enlarged into 13-man assault teams. Weeks before the invasion, all available demolition men were sent from Fort Pierce to England. By June 1944, 32 NCD Units were deployed in England.


The Germans had constructed intricate defenses on the French coastline. These included steel posts driven into the sand and topped with explosives. Large 3-ton steel barricades called Belgian Gates were placed well into the surf zone. Reinforced mortar and machine gun nests were spotted along the beaches.

The Naval Scouts spent weeks gathering information during nightly surveillance missions up and down the French coast. Replicas of the Belgian Gates were constructed on the south coast of England for the NCDUs to practice demolitions. It was possible to blow a gate to pieces, but that only created a mass of tangled debris spread along the beaches, thereby creating more of an obstacle. The NCDU found that the best method was to sever the key corner joints in a gate, so that it fell down flat.

According to the Allied attack plans, infantry supported by naval gunfire would make the initial landings, followed by tanks and troop carriers to clear any remaining German bunkers and snipers. The NCDU members (designated Demolitions Gap-Assault teams comprised of Army Combat Engineers and Navy Combat Demolition personnel, on Omaha, with a counterpart, Beach Obstacle Demolition Parties on Utah) would come in with the second wave and work at low tide to clear the obstacles. Their mission was to open sixteen 50-foot (15 m) wide corridors for the landing at each of the U.S. landing zones (Omaha Beach and Utah Beach).

Unfortunately, the plans could not be executed as laid out. The preparatory air and naval bombardment was ineffective, leaving many German guns in position to fire on the attackers. Also, tidal conditions caused many of the NCDU teams to land prematurely - in some cases ahead of the first wave. Despite heavy German fire and resulting casualties, the NCDU men planted charges and demolished many obstacles. As the infantry came ashore, some soldiers took cover on the seaward sides of obstacles that had demolition charges on them. They quickly moved onto the beach.

The greatest difficulty was at Omaha Beach. By nightfall only thirteen of the planned sixteen gaps were open, and of the 175 NCDU men who went ashore there, 31 were killed and 60 were wounded.

The attack on Utah Beach was much more successful. There, only 2 were killed and 14 wounded, when an artillery shell hit a team working to clear the beach.[4]

NCDUs also participated in Operation Dragoon, the invasion of southern France.

NCDUs also served in the Pacific theater. NCDUs 2 and 3 were transferred there, and shortly thereafter joined by three other units. These 5 units would serve the duration of the war in the Pacific, augmented by a veteran unit from Omaha beach.

Kauffman, later 'augmented' to a regular Navy commission, went on to a long and illustrious Navy career, including service as Superintendent of the Naval Academy. He retired as a Rear Admiral in 1973.


The first UDTs to use that designation were formed exclusively for deployment in the Pacific Theater.


The invasion of Tarawa in November 1943 nearly met disaster due to obstacles in the surf. Tarawa lies in eastern Micronesia. The islands in this region have unpredictable tides and are surrounded by shallow reefs that block even shallow-draft craft, except at a few narrow channels or at high tide. At Tarawa, the attack went in at low tide, due to inadequate knowledge of local conditions, and the surrounding reefs were exposed. The Amtracs carrying the first wave crossed the reef successfully. But the LCVPs carrying the second wave ran aground on the reef. The Marines had to unload and wade to shore. Many drowned or were killed before making the beach. The first wave, fighting without reinforcements from the second wave, took heavy losses on the beach. It was a painful lesson that the Navy would not permit to be repeated.

Admiral Kelly Turner, the Navy's top amphibious expert, ordered the formation of nine Underwater Demolition Teams. As with the NCDUs in Europe, the personnel for these teams were mostly Seabees. These volunteers were organized into Combat Swimmer Reconnaissance Units, becoming the Navy UDTs.[6]


UDT training was at Waimānalo, Hawai'i on Oahu under the aegis of V (Fifth) Amphibious Force. Among both instructors and trainees, there were graduates of the Fort Pierce school Navy Combat Demolition Unit Project, Marines, and Army soldiers. Under the direction of Marine Amphibious Reconnaissance Company, they hastily trained for the attack on Kwajalein on 31 January 1944.[10]

The training made use of inflatable boats and included surprisingly little swimming. The men were expected to paddle in, and work in shallow water, leaving the deep-water demolitions to the Army. Marine Reconnaissance units would conduct the hydrography from shallow water to inland while the accompanying UDT would conduct the demolition and hydrography from near-deep water to the shallows.

The UDTs were organized with approximately sixteen officers and eighty men each. One Marine and one Army officer were liaisons within each team.[11] It became apparent that a UDT assigned to the same beach as a Marine unit should be embarked in the same high speed transport (APD).

At this point, the men wore Navy fatigues with shoes and helmets. They were life-lined to their boats and stayed out of the water as much as possible. The plan was to send in night reconnaissance teams such as the Scouts and Raiders were accustomed to. Then Admiral Turner, worried about the obstacles placed by the Japanese, ordered two daylight reconnaissance operations at Kwajalein.

The missions were to follow the standard procedure. Each two-man team was to paddle close to the beach in a rubber boat, wearing full fatigues, boots, life jackets, and metal helmets, and then make their observations. But Team 1 found that the coral reef kept their craft too far from shore to be certain of the beach conditions. and Chief Petty Officer Bill Acheson, quite accustomed to operating in swim trunks or skivvies, and Ensign Lewis F. Luehrs stipped off the combat fatigues and swam undetected across the reef. They returned with sketches of gun emplacements and locations, information about a log wall built to deter landings, and other vital intelligence. This was a major turning point for the tactics of the UDT. Combat swimming had now entered the Mission Essential Task List of the UDT.

After Kwajalein, the UDT created the Naval Combat Demolition Training and Experimental Base at Kihei, next to the Amphibious Base at Kamaole on Maui. Operations began in February 1944. In April, Draper Kauffman was transferred from Fort Pierce to command UDT 5 and serve as senior staff officer, Underwater Demolition Teams, Amphibious Forces, and Underwater Demolition Training Officer, Amphibious Training Command.

Most of the procedures from Fort Pierce had been modified, with importance placed now upon developing strong swimmers. Extensive training was conducted in the water without lifelines, using facemasks, and wearing only swim trunks and fins. This new model created the image that stands today of the UDT as the "Naked Warriors".

Eventually, 31 UDT teams were commissioned. These "Naked Warriors" saw action across the Pacific in every major amphibious landing.


The landings continued. Kauffman led UDT 5, in conjunction with UDT 3, 4, 6 and 7, in daylight recon of the defenses of Saipan and in a night recon of the defenses of Tinian, followed by work at Guam. UDT 15 reconnoitered beaches at Luzon in the Philippines. UDT 15 also reconnoitered Iwo Jima, two days ahead of the invasion. The UDT suffered only one man wounded in action. However, the next day a Japanese plane bombed their APD, USS Blessman. 15 men of UDT 15 were killed, and 23 were injured. This was the single largest loss of life suffered by the UDTs in the Pacific theater.

UDTs also served at Eniwetok, Guam, Angaur, Ulithi, Peleliu, Leyte, Lingayen Gulf, Zambales, Labuan, and Brunei Bay. The last UDT demolition operation of the war was on 4 July 1945 at Balikpapan, Borneo.

The largest UDT operation was in support of the invasion of Okinawa, in March 1945. Veteran UDTs 7, 12, 13, and 14, and newly trained UDTs 11, 16, 17, and 18 participated: nearly 1,000 men.

Up to this time, all UDT missions in the Pacific had been in warm tropical waters. Now the forces moved north toward Japan. The waters around Okinawa are not cold, but they are cool enough that long immersion can cause hypothermia and severe cramps. Having no thermal protection, the UDT men were at risk of these effects during the operations around of Okinawa.

Operations included both real reconnaissance and demolition at the actual invasion site, and feints to create the illusion of landings in other locations. Pointed poles set into the coral reef of the beach protected the landing beaches on Okinawa. UDTs 11 and 16 were sent in to blast the poles. After all the charges were set, the men swam clear. The explosions took out all of UDT 11's targets and half of UDT 16's. UDT 16 aborted the operation due to the death of one of their men. UDT 16's executive officer and a platoon returned with the assistance of some from UDT 11 the following day to finish the job, and then remained to guide the forces to the beach.

The UDTs continued to prepare for the invasion of Japan until Japan surrendered in August 1945, and their role in the Pacific came to an end. Within months of the war's end, the most of the men of the UDT teams were discharged, athough a remnant remained in training at Coronado. This ended a trying but evolutionary time in the history of Naval Special Warfare.[4]

After World War II

Two half-strength UDTs were retained, one on each coast. Though no combat operations seemed likely, the UDTs continued to research new techniques for underwater and shallow-water operations.

One area was the use of SCUBA equipment.

Dr. Chris Lambertsen had developed the Lambertsen Amphibious Respiratory Unit (LARU), an oxygen rebreather, which was used by the Maritime Unit of the OSS. In October 1943, he demonstrated it to LCDR Kauffman, but was told there was no place in current UDT operations for this radically new device.[12][13]

However, Dr. Lambertsen and the OSS continued to work on closed-circuit oxygen diving and combat swimming. When the OSS was dissolved in 1945, Lambertsen retained the LARU inventory. He later demonstrated the LARU to Army Engineers, the Coast Guard, and the UDTs. In 1947, he demonstrated the LARU to LCDR Francis "Doug" Fane, then a senior UDT commander.[12][14]

LCDR Fane was enthusiastic for new diving techniques. He pushed for the adoption of rebreathers and SCUBA gear for future operations. But the Navy Experimental Diving Unit and the Navy Dive School (which used the old "hard-hat" diving apparatus) declared it was too dangerous. Nonetheless, Fane invited Dr. Lambertsen to NAB Little Creek, Virginia in January 1948 to demonstrate and train UDT personnel in SCUBA operations. This was the first-ever SCUBA training for Navy divers. Following this training, Fane and Lambertsen demonstrated new UDT capabilities with a successful lock-out and re-entry from USS Grouper (SS-214), an underway submarine, to show the Navy's need for this capability. LCDR Fane then started the classified “Submersible Operations” or SUBOPS platoon with men drawn from UDT 2 and 4 under the direction of LTJG Bruce Dunning.[12][15]

LCDR Fane also brought the conventional "Aqua-lung" open-circuit SCUBA system into use by the UDTs. Open-circuit SCUBA is less useful to combat divers, as the exhausted air produces a tell-tale trail of bubbles. However, in the early 1950s, the UDTs decided they preferred open-circuit SCUBA, and converted entirely to it. (The remaining stock of LARUs was supposedly destroyed in a beach-party bonfire.) Later on, the UDT reverted to closed-circuit SCUBA, using improved rebreathers developed by Lambertsen.

It was at this time that the UDT (led by Fane) established training facilities at Saint Thomas in the Virgin Islands.[16]

The UDT also began developing weapons skills and procedures for commando operations on land in coastal regions. The UDT started experiments with insertion/extraction by helicopter, jumping from a moving helicopter into the water or rappelling like mountain climbers to the ground. Experimentation developed a system for emergency extraction by plane called "Skyhook." Skyhook utilized a large helium balloon and cable rig with harness. A special grabbing device on the nose of a C-130 enabled a pilot to snatch the cable tethered to the balloon and lift a person off the ground. Once airborne, the crew would winch the cable in and retrieve the personnel though the back of the aircraft. This technique was discontinued for training purposes after the death of a SEAL at NAB Coronado on a training lift. The teams still utilize the Fulton Skyhook for equipment extraction and retain the capability for war if an extreme situation requires it.

Korean War

During the Korean War, the UDTs operated on the coasts of North Korea, with their efforts initially focused on demolitions and mine disposal. Additionally, the UDT accompanied South Korean commandos on raids in the North to demolish railroad tunnels and bridges. The higher-ranking officers of the UDT frowned upon this activity because it was a non-traditional use of the Naval forces, which took them too far from the water line. Due to the nature of the war, the UDT maintained a low operational profile. Some of the better-known missions include the transport of spies into North Korea, and the destruction of North Korean fishing nets.

A more traditional role for the UDT was in support of Operation CHROMITE, the amphibious landing at Inchon. UDT 1 and UDT 3 divers went in ahead of the landing craft, scouting mud flats, marking low points in the channel, clearing fouled propellers, and searching for mines. Four UDT personnel acted as wave-guides for the Marine landing.[17]

The UDT assisted in clearing mines in Wonsan harbor, under fire from enemy shore batteries. Two minesweepers were sunk in these operations. A UDT diver dove on the wreck of USS Pledge: the first U.S. combat operation with SCUBA.

The Korean War was a period of transition for the men of the UDT. They tested their previous limits and defined new parameters for their special style of warfare. These new techniques and expanded horizons positioned the UDT well to assume an even broader role as the storms of war began brewing to the south in Vietnam.[18]


The Navy entered the Vietnam War in 1958, when the UDTs delivered a small watercraft far up the Mekong River into Laos. In 1961, Naval advisers started training the South Vietnamese UDT. These men were called the Liên Đoàn Người Nhái (LDNN), roughly translated as the "soldiers that fight under the sea."

The UDT also carried out hydro-graphic surveys in South Vietnam's coastal waters.[19]

Later, the UDTs supported the Amphibious Ready Groups operating on South Vietnam's rivers. UDTs manned riverine patrol craft and went ashore to demolish obstacles and enemy bunkers. These Detachments operated throughout South Vietnam, from the Mekong Delta (Sea Float), The Parrot Beak and French canal AO's through I Corp and the Song Cui Dai Estuary south of Danang.

Birth of Navy SEALs

In the mid-1950s, the Navy saw how the UDT's mission had expanded to a broad range of "unconventional warfare", but also that this clashed with the UDT's traditional focus on swimming and diving operations. It was therefore decided to create a new type of unit that would build on the UDT's elite qualities and water-borne expertise, but would add land combat skills, including parachute training and guerrilla/counterinsurgency operations.[20] These new teams would come to be known as the US Navy SEALs (which stood for SEa, Air, and Land). Initially there was a lag in the unit's creation until President John F. Kennedy took office. Kennedy recognized the need for unconventional warfare, and supported the use of special operations forces against guerrilla activity. The Navy moved forward to establish its new special operations force and in January 1962, SEAL Team One was commissioned. The SEALs quickly earned a reputation for valor and stealth in Vietnam, where they conducted clandestine raids in perilous territory. Since then, teams of SEALs have taken on shadowy missions in strife-torn regions around the world, stalking high-profile targets such as Panama's Manuel Noriega and Colombian drug lord Pablo Escobar and playing integral roles in the wars in Iraq and Afghanistan.[21] .[22]


Underwater Demolition Badge

For those who served in an Underwater Demolition Team, the U.S. Navy authorized the Underwater Demolition Badge. The badge was phased out in 1983 with the disbandment of the UDT.


  • The Frogmen (1951). This film starring Dana Andrews and Richard Widmark was based on the UDT teams. The film was set in World War II, and contemporary UDT members appeared in several sequences.
  • Without Remorse (1993), a novel by Tom Clancy. The protagonist, John Kelly, is a former UDT and SEAL.

See also


  2. 2.0 2.1 2.2 2.3 Cunningham, Chet (2004). The Frogmen of World War II: An Oral History of the U.S. Navy's Underwater Demolition Teams. Pocket Star. ISBN 978-0-7434-8216-5.'s%20Underwater%20Demolition%20Teams&pg=PA3#v=onepage&q&f=false. 
  3. "Navy SEAL History". Retrieved 25 January 2008. 
  4. 4.0 4.1 4.2
  6. 6.0 6.1 Bruce Meyers, Swift, Silent, and Deadly: Marine Amphibious Reconnaissance in the Pacific, 1942-1945, 2004
  7. p.34 Dockery, Kevin & Brutsman, Bud Navy SEALs A History of the Early Years Berkely Publishing 2001
  8. p.p 30-31 Dockery & Brutsman
  10. "Bruce F. Meyers, Swift, Silent, and Deadly"
  11. Commander, V Amphibious Corps to CinCPac, report, Underwater Demolition Teams, Recommendations Concerning-Based on Experience in Flintlock (Kwajalein), 2 June 1944, declassified from secret.
  12. 12.0 12.1 12.2 Butler FK (2004). "Closed-circuit oxygen diving in the U.S. Navy". pp. 3–20. PMID 15233156. Retrieved 18 March 2009. 
  13. Hawkins T (1st Quarter 2000). "OSS Maritime". 
  14. Vann RD (2004). "Lambertsen and O2: beginnings of operational physiology". pp. 21–31. PMID 15233157. Retrieved 18 March 2009. 
  15. Vann RD (Spring 2000). "The evolution of diving in UDT from WW II through Korea.". 
  16. "CMDR. DOUG FANE NAVY UDT LEADER". Retrieved 6 December 2009. 
  18. "Navy UDT-SEAL Museum:History,Korea". Retrieved 25 January 2008. 
  20. Boynton, Mack (2010). A Founding Father of the Navy SEALs. 
  21. Altman, Alex (Apr 27, 2009). "A Brief History of: The Navy SEALs".,9171,1891738,00.html. Retrieved 12 May 2013. 
  22. , Mack Boynton (4th Quarter 2007). "SEAL Story of - SEAL Teams". UDT-SEAL Association. Retrieved 6 December 2009. 

External links

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