Underwater Demolition Teams
Underwater Demolition Teams shoulder sleeve patch.JPG
Patch of the Underwater Demolition Teams.
Active15 August 1942 – 1 January 1983
CountryUnited States
BranchUnited States Navy
TypeAmphibious warfare
Garrison/HQFort Pierce, Florida, U.S.
Maui, Hawaii, U.S.
Nickname(s)UDT, The Frogmen
EngagementsOperation Overlord
Battle of Iwo Jima
Battle of Okinawa
Operation Torch
Borneo campaign
Battle of Peleliu
Battle of Saipan
Battle of Tinian
Battle of Guam
Battle of Leyte
Invasion of Lingayen Gulf
Korean War
Vietnam War
UDT Memorial at Bellows AFB take in October 2016.[1]

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 splash down in the Mercury program through Apollo manned space flight programs.[2]

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.[3]

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.[4]

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 to Army Second Lieutenant Lloyd E. Peddicord being assigned the task of analyzing the need for a human intelligence (HUMINT) capability.[3]

When the U.S. entered World War II, the Navy 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 Raiders, at the amphibious training base at Little Creek, Virginia.[3]

In 1942, the Army and Navy jointly established the Amphibious Scout and Raider School at Fort Pierce, Florida. Here Lieutenant Commander Phil H. Bucklew, the "Father of Naval Special Warfare", helped organize and train what became the Navy's 'first group' to specialize in amphibious raids and tactics.

Pressure to further implement human intelligence gathering prior to landings heightened after Naval amphibious 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. Sailors and Marines were forced to abandon their craft in chest deep water a thousand yards from shore, helping Japanese gunners inflict heavy U.S. casualties.[3] After that experience, Rear admiral Kelley Turner, Commander of the V Amphibious Corps (VAC), directed that 30 officers and 150 enlisted men be moved to Waimanalo ATB (on the island of Oahu) to form the nucleus of a reconnaissance and demolition training program. It is here that the UDTs of the Pacific were born.[5]

Later in war, the Army Engineers passed down demolition jobs to the U.S. Navy. It then became the Navy's responsibility to clear any obstacles and defenses in the near shore area.[citation needed]

A memorial to the founding of the UDT has been built at Bellows Air Force Station near the original Amphibious Training Base (ATB) Waimanalo.

Naval Combat Demolition Units

U.S. Naval Combat Demolition insignia. – U.S. Navy Seal Museum

In early 1942 it became apparent that the Navy needed that capability to destroy submerged obstacles, natural or man-made, for amphibious landings. 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.

In early May 1943, a two-phase "Naval Demolition Project" was directed by the Chief of Naval Operations (CNO) "to meet a present and urgent requirement". The first phase began at Amphibious Training Base (ATB) Solomons, Maryland with the establishment of Operational Naval Demolition Unit No. 1. Six Officers and eighteen enlisted men reported from NTC Camp Peary dynamiting and demolition school for a four-week course.[7][8] Those Seabees were immediately sent to participate in the invasion of Sicily[9] where they were divided in three groups that landed on the beaches near Licata, Gela and Scoglitti.[10]

Later in 1943 the Navy decided to create a component dedicated to eliminating amphibious obstructions. They were called Naval Combat Demolition Units (NCDU) consisting of one junior Civil Engineer Corps (CEC) officer and five enlisted men. A NCDU was to clear beach obstacles for an invasion force with the team coming ashore in an LCRS inflatable boat.[11] On May 7, Admiral Ernest J. King, the CNO, picked Lieutenant Commander Draper L. Kauffman USNR to lead the training. The first six classes graduated from "Area E" at NTC Camp Peary.[12] From there the NCDU training was moved to Fort Pierce. Despite the move, Camp Peary was Kauffman's source of manpower. "He would go up to Camp Peary and the Dynamite School, assemble the (Seabees) in the auditorium and say, 'I need volunteers for hazardous, prolonged and distant duty.'"[13] Most of Kauffman's volunteers came from the Seabees (the Navy's Construction Battalions), the U.S. Marines, and U.S. Army combat engineers. Training commenced with one grueling week designed to "separate the men from the boys". Some said that "the men had sense enough to quit, leaving Kauffman with the boys."[14] It was and is still considered the first "Hell Week."


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 Operation Overlord. All told, the NCDUs had 34 teams in England for the invasion of Normandy. While waiting for D-day the NCDUs trained with the 146th, 277th and 299th Combat Engineer Battalions.[15] Each NCDU had 5 men from a Combat Engineer Battalion attached to the team. In the beginning the first 10 NCDUs were split into 3 groups.[15] Initially it was somewhat ad-hoc as they had no Commanding Officer, but the Senior officer was the leader of group III, Lieutenant Smith (CEC). He served in that capacity unofficially for the entire group.[15] His group III performed numerous experimental demolitions work and developed the Hagensen Pack.[15](an innovation that used 2.5-pound (1.1 kg) of tetryl placed into rubber tubes that could be twisted around obstacles)[16] As more teams arrived a NCDU Command was created for the invasion. The NCDUs at Normandy were numbers: 11, 22-30, 41-46, 127-8, 130-42[15]

"NCDU 45"; Ensign Karnowski, Chief Carpenters Mate Conrad C. Millis, MM2 Equipment Operator Lester Meyers and three sailors. The unit received a Presidential Unit Citation with Ens. Karnowski earning the Navy Cross & French Croix de Guerre with Palm, while MM2 Meyers received a Silver Star.

The Germans had constructed intricate defenses on the French line. 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 dotted along the beaches.

The Scouts and Raiders 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 on. 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 teams (designated Demolitions Gap-Assault teams) 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 on 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 four were killed and eleven wounded, when an artillery shell hit a team working to clear the beach.[5] Overall, NCDUs had 53 percent casualties.

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

With Europe invaded most of the NCDUs were sent to Fort Pierce and integrated into the UDTs for the Pacific campaign. However, the first NCDUs, 1-10, had been staged at Turner City, Florida Island in the Solomon Islands during January 1944.[17] A few were temporarily attached to UDTs.[17] Later NCDUs 1-10 were combined to form Underwater Demolition Team Able.[17] This team was disbanded with NCDUs 2 and 3, plus three others assigned to MacArthur's 7th Amphibious force, and were the only NCDUs remaining at war's end. The other men from Team Able were assigned to numbered UDTs.

Underwater Demolition Teams

The first units that were designated as Underwater Demolition Teams were formed in the Pacific Theater. Rear Admiral 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. UDT training was at Waimānalo, Hawaii, on Oahu under the aegis of V Amphibious Corps. Among both instructors and trainees, there were graduates of the Fort Pierce schools (Scouts and Raiders, and NCDU men), Seabees, Marines, and Army soldiers. Under the direction of Marine Corps Amphibious Reconnaissance Battalion, they hastily trained for the attack on Kwajalein, 31 January 1944.[6] The training made use of inflatable boats and included some 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. At that time the men in the teams wore Navy fatigues with boots and helmets. They were lifelined to their boats and stayed out of the water as much as possible.

The UDTs were organized with approximately sixteen officers and eighty men each. One Marine and one Army officer were liaisons within each team.[18] 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). The UDTs were deployed in every major amphibious landing in the Pacific with 34 teams eventually being established. The last teams created for the invasion of Japan were spared deployment by the atomic bombing of Japan. When it was over, teams 1-21 were the teams utilized operationally, meaning that slightly over half of the operational UDTs came from the Seabees.

Prior to Operation Galvanic and Tarawa, V Amphibious Corps had identified coral as an issue for future amphibious operations. Rear Admiral Turner, Commander, V Amphibious Corps, had ordered a review to address the problem. VAC found that the only people having any applicable experience with the material were men in the Naval Construction Battalions. The Admiral tasked LT T.C. Crist (CEC) to develop a method for blasting coral under combat conditions and putting together a team for that purpose.[19] LT Crist started by contacting others he had blasted coral with in CB 5 and by the end November 1943 he had assembled close to 30 officers and 150 enlisted men, at Waipio Amphibious Operating Base on Oahu.[19]


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, an unusual neap tide occurred, leaving insufficient clearance for the Higgins boats (LCVPs) to get over the reef. 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 several hundred yards across the lagoon to shore while wearing full packs, under constant heavy fire from shore defenses. 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.


The next objective was Kwajalein and the original plan called for night reconnaissance. However, Rear Admiral Turner did not want a repeat of Tarawa and wanted to know about the coral as well ad any obstacles the Japanese may have emplaced. To find this out, UDT 1 was ordered to perform two daylight recons.[20] In keeping with the Seabee traditions of: (1) doing whatever it takes to accomplish the job and (2) not always following military rules to get it done, UDT 1 did both. The missions were to follow the standard procedure with each two-man team getting 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. Ensign Lewis F. Luehrs and Seabee Chief Bill Acheson had anticipated that they would not be able to carry out the assignment following the Fort Pierce model and had worn swim trunks beneath their fatigues.[20] Stripping down, they swam 45 minutes undetected across the reef. When they returned with sketches of gun emplacements and other vital intelligence, they were taken, still in their trunks, directly to Rear Admiral Turner's flagship to report.[20] Afterwards Admiral Turner concluded that the only way to get this kind of information was from individual swimmers, and he relayed those thoughts to Admiral Nimitz, Commander-in-Chief, U.S. Pacific Fleet. The planning and decisions of Rear Admiral Turner, Ensign Lehrs and Chief Achenson made Kwajalein a transition point in UDT history, changing both the mission model and training regimen. Seabees made up the majority of the men in teams 1–9 and 13. The Officers of those teams were primarily CEC[21] (Seabees). After Kwajalein, the UDTs created the Naval Combat Demolition Training and Experimental Base at Kihei, next to the Amphibious Base at Kamaole on Maui, expanding upon what had been learned from UDT 1. Operations began in February 1944. Most of the procedures from Fort Pierce were changed. They were replaced with an emphasis on developing strong swimmers, daylight reconnaissance, and training without lifelines. The uniform of the day changed to diving masks, swim trunks, fins and a Ka-bar knife, creating the image of the UDTs as the "Naked Warriors."

Peleliu, Philippines, Guam, and Iwo Jima

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.

UDTs 6 & 7 drew the Peleliu assignment while UDT 8 went to Angaur. The officers were almost all CEC and the enlisted men were Seabees.[22]

UDT 10 was directly under the Office of Strategic Services (OSS)[citation needed]. It had a secret base on Santa Catalina Island, California, before the Maui base was operational. When the team was being formed it was joined by five officers and 21 men who had been trained by the OSS. They were led by a LT A.O. Chote Jr., who became UDT 10's commanding officer.

UDT 14 was the first all-Navy team (one of three from the Pacific fleet).

Seabees in both UDT 3 & UDT 4 made these welcome signs for the U.S. Marine Corps on Guam.

The landings in the Pacific Theater continued and Kauffman led UDT 5 in a daylight recon of the defenses of Saipan and in a night recon of the defenses of Tinian. Two days ahead of the invasion of Iwo Jima UDTs 12, 13, 14, and 15 reconnoitered the beaches suffering only one man wounded. However, the next day a Japanese plane bombed UDT 15's APD, USS Blessman. Fifteen men were killed, and 23 were injured. This was the single largest loss of life suffered by the UDTs. At Iwo Jima the teams not only did reconnaissance but on D-plus 2 were called upon to help clear the beaches of broached or damaged landing craft. The water's edge had become so clogged with debris that there was no place for landing craft to get ashore. Later UDT 15 reconnoitered beaches at Luzon in the Philippines.

UDTs also served at Eniwetok, Ulithi, 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, totalling nearly 1,000 men in all. Up to that time, all UDT missions in the Pacific had been in warm tropical waters. Now the forces moved north toward Japan where the waters around Okinawa were cool enough that long immersion could cause hypothermia and severe cramps. Since they wore no thermal protection at that time, the UDTs were at risk to these hazards during their operations around 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; hence, their mission was considered a failure. UDT 11 was sent back 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, a majority of the UDT teams were deactivated and only two partial teams remained, thus ending an evolutionary time in the history of Naval Special Warfare.[5]


LCDR Edward P. Clayton, (back to camera) Commanding Officer UDT 21, receiving the first sword surrendered to an American force in the Japanese Home islands, from a Japanese Army Coastal Artillery Major (opposite Clayton), at Futtsu-misaki Point, across Tokyo Bay from Yokosuka Naval Base, 28 August 1945. When word of this circulated LCDR Clayton was ordered to give up the sword. Protocol dictated that General MacArthur should receive the first surrendered sword.

On 20 August 1945 USS Begor embarked UDT 21 at Guam as a component of the U.S. occupation force heading for Japan.[23] Nine days later UDT 21 became the first U.S military unit to set foot on Japanese home soil when it reconned the beaches at Futtsu-misaki Point in Tokyo Bay.[23] The assessment was that the area was well suited for landing U.S. amphibious forces. The next day Begor took UDT 21 to Yokosuka Naval Base.[23] There the team cleared the docks for the first U.S. warship to dock in Japan, USS San Diego.[23] The team remained in Tokyo Bay until 8 Sept when it was tasked with locating remaining Kamikaze and two man submarines at Katsura Wan, Uchiura Wan at Suruga Bay, Sendai, Onohama Shipyards and Choshi.[23]. Orders arrived for Begor to return the team to San Diego on 27 September[23].

After World War II

With the draw-down from the war two half-strength UDTs were retained, one on each coast.

Operation Crossroads

Bikini atoll was chosen for the site of the nuclear tests of Operation Crossroads.

"In March 1946, Project Y scientists from Los Alamos decided that the analysis of a sample of water from the immediate vicinity of the nuclear detonation was essential if the tests were to be properly evaluated. After consideration of several proposals to accomplish this, it was finally decided to employ drone boats of the type used by Naval Combat Demolition Units in France during the war"[24].

UDT Easy, later named UDT 3, was given the designation TU 1.1.3 for the Operation and was assigned the control and maintenance of the drone boats. On 27 April, 7 officers and 51 enlisted men embarked Begor at the Seabee base Port Hueneme, CA,[25] for transit to Bikini. At Bikini the drones were controlled from Begor. Once a water sample was taken the drone would return to Begor to be hosed down for decontamination. After a Radiation Safety Officer had taken a Geiger counter reading and the OK given, the UDTs would board with a radiation chemist to retrieve the sample.[26] Begor came to have the reputation as the most contaminated boat in the fleet.[27]

A major issue afterwards was the treatment of the dislocated natives. In November 1948, the Bikinians were relocated to the uninhabited Island of Kili, however that island was located inside a coral reef that had no channel for access to the sea.[28] In the spring of 1949, the Governor of the Trust Territories, Marshall Group requested the U.S. Navy blast a channel to change this.[28] That task was given to the Seabees on Kwajalin whose CO quickly determined this was actually a UDT project.[28] He sent a request to CINCPACFLT who forwarded it to COMPHIBPAC.[28] This ultimately resulted in the sending of UDT 3 on a Civic action program that turned out better than politicians could have hoped. The King of the Bikinians held a send off feast for the UDTs the night before they departed.[28]

Submersible Operations

Even 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.[29][30] 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.[29][31] 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 the new equipment be too dangerous. Nonetheless, LCDR 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, LCDR Fane and Dr. Lambertsen demonstrated new UDT capabilities with a successful lock-out and re-entry from USS Grouper, 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 Lieutenant (junior grade) Bruce Dunning.[29][32]

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.[citation needed] Later on, the UDT reverted to closed-circuit SCUBA, using improved rebreathers developed by Dr. Lambertsen.

It was at this time that the UDT, led by LCDR Fane, established training facilities at Saint Thomas in the Virgin Islands.[33]

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 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.[34]

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 using SCUBA gear.

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 war began brewing to the south in Vietnam.[35]

Vietnam War

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 UDT in South Vietnam. The men were called the Liên Đoàn Người Nhái (LDNN), roughly translated as the "soldiers that fight under the sea."

The UDT also carried out hydrographic surveys in South Vietnam's coastal waters.[36]

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. They operated throughout South Vietnam, from the Mekong Delta (Sea Float), The Parrot Beak and French canal AO's through I Corps 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.[37] These new teams would come to be known as the US Navy SEALs, an acronym 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 commissioned SEAL Team ONE in NAB Coronado and SEAL Team TWO at NAB Little Creek. UDT-11 & 12 were still active on the west coast and UDT-21 & 22 on the east coast. The SEALs quickly earned a reputation for valor and stealth in Vietnam, where they conducted clandestine raids in perilous territory. In May 1983, the remaining UDT teams were reorganized as SEAL teams. UDT 11 became SEAL Team Five and UDT 12 became Seal Delivery Vehicle Team One. UDT 21 became SEAL Team Four and UDT 22 became Seal Delivery Vehicle Team Two. A new team, SEAL Team Three was established in October 1983. Since then, teams of SEALs have taken on clandestine missions in war-torn regions around the world, tracking 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.[38][39]


UDT Badges
Officer Underwater Demolition Badge
Enlisted Underwater Demolition Badge

For those who served in an Underwater Demolition Team, the U.S. Navy authorized the Underwater Demolition operator badge in 1970. However, the UDT badge was phased out in 1971, a few months after it appeared, as was the silver badge for enlisted UDT/SEAL frogmen. After that, SEAL and UDT operators, both officer and enlisted, all wore the same gold Trident, as well as gold Navy jump wings. [40]

Unit awards

The UDTs have received several unit citations and commendations. Members who participated in actions that merited the award are authorized to wear the medal or ribbon associated with the award on their uniform. Awards and decorations of the United States Armed Forces have different categories, (i.e. Service, Campaign, Unit, and Personal). Unit Citations are distinct from the other decorations.[41]

Naval Combat Demolition Force O (Omaha beach) Normandy

Naval Combat Demolition Force U (Utah beach) : Normandy




UDT 11

UDT 12

UDT 13

UDT 14

UDT 21

UDT 22



  • The Frogmen (1951), starring Dana Andrews and Richard Widmark. World War II film based on the Underwater Demolition Teams. Contemporary UDT members appear in several sequences.[citation needed]

See also


  1. ^ "Commemorating The Birthplace of UDT-SEAL Teams: Waimanalo, Hawaii | National Navy UDT-SEAL Museum". Navysealmuseum.com. 11 November 2013. Retrieved 12 May 2014.
  2. ^ "SEAL History: Before the First Mercury Splashdown | National Navy UDT-SEAL Museum". Navysealmuseum.com. Retrieved 12 May 2014.
  3. ^ a b c d 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.
  4. ^ "Navy SEAL History". Retrieved 25 January 2008.
  5. ^ a b c "SEAL History: Origins of Naval Special Warfare-WWII | National Navy UDT-SEAL Museum". Navysealmuseum.com. Retrieved 12 May 2014.
  6. ^ a b Meyers, Bruce F. (2004). Swift, Silent, and Deadly: Marine Amphibious Reconnaissance in the Pacific, 1942–1945. Naval Institute Press.
  7. ^ Blazich, Frank A. (12 May 2017). "This Week in Seabee History (Week of May 14)". Seabee Online. Navy Facilities Engineering Command. Retrieved 18 October 2017.
  8. ^ Blazich, Frank A. (6 June 2014). "Opening Omaha Beach: Ensign Karnowski and NCDU-45". Seabee Online. Navy Facilities Engineering Command. Retrieved 18 October 2017.
  9. ^ "Seal History: Origins of Naval Special Warfare – WWII". Navy Seal Museum Archives. Retrieved 18 October 2017.
  10. ^ pp. 30-31 Dockery & Brutsman
  11. ^ p.34 Dockery, Kevin & Brutsman, Bud Navy SEALs A History of the Early Years Berkely Publishing 2001
  12. ^ "Naval Combat Demolition Units". SpecWarNet.net. Retrieved 1 March 2018.
  13. ^ Erickson, Mark St. John (3 December 2017). "Training the Fighting Seabees of WWII at Camp Peary". Daily Press. Newport News, Virginia.
  14. ^ Hornfischer, James D. (2017). The Fleet at Flood Tide: America at Total War in the Pacific, 1944–1945. New York: Bantam Books. p. 44.
  15. ^ a b c d e REPORT ON NAVAL COMBAT DEMOLITION UNITS in OPERATION "NEPTUNE" as part of TASK FORCE 122, Submitted by: Lt.(jg) H. L. Blackwell, Jr. D-V(G) , USNR, 5 July, 1944
  16. ^ "World War II Era Beach Obstacles and Hedgehogs from Original NCDU School | National Navy UDT-SEAL Museum". NavySealMuseum.com. Retrieved 12 May 2014.
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  40. ^ Special Warfare insignia
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Further reading

  • Best, Herbert. The Webfoot Warriors; The Story of UDT, the U.S. Navy's Underwater Demolition Team. New York: John Day Co, 1962. OCLC 1315014
  • Fane, Francis Douglas, and Don Moore. The Naked Warriors: The Story of the U.S. Navy's Frogmen. Annapolis, MD: Naval Institute Press, 1995. ISBN 1557502668 OCLC 33007811
  • O'Dell, James Douglas. The Water Is Never Cold: The Origins of the U.S. Navy's Combat Demolition Units, UDTs, and SEALs. Washington, DC: Brassey's, 2000. ISBN 1574882759 OCLC 44764036
  • Young, Darryl. SEALs, UDT, Frogmen: Men Under Pressure. New York: Ivy Books, 1994. ISBN 0804110646 OCLC 31815574

External links

  • Navy UDT-SEAL Museum
  • NavyFrogMen.com U. S. Naval Special Warfare Archives
  • Pritzker Military Museum & Library
  • "TNT Divers" Popular Mechanics, November 1945, pp. 72–73, one of earliest articles on WW2 UDT units.