Although Army and Marines engineers and special battalions have long been trained in the clearance of mine fields and in the removal of booby traps and other devices to impede the forward movement of troops, until recently (Editor's note: this was written during the war) no trained personnel have been available to remove underwater obstacles designed to hinder or prevent the landing of troops on enemy beaches. Amphibious operations prior to Tarawa were fortunately not seriously hampered by this lack of personnel since, according to information presently available, neither the Germans nor the Italians in North Africa, Sicily, or Salerno, nor the Japanese in the South Pacific, made extensive use of man made underwater obstacles. Tarawa, however was an entirely different story and that campaign proved that properly trained naval combat demolition personnel were vitally needed in future amphibious operations both for reconnaissance work and for the removal of obstacles.

Previous to Tarawa, there had been some preliminary work accomplished. A few officers and men had been given rudimentary underwater demolition training for European operations at the Solomons, Maryland, and were available for, but not used in the Sicilian campaign. In July, 1943, a program for training personnel in naval combat demolition was established at the Amphibious Training Base, Fort Pierce, Florida. The course given at Fort Pierce was apparently designed to train small units (one officer and five men in each unit) for rubber boat reconnaissance work at night and for demolition of man-made .... (obstacles) was based on British methods for cross-channel operations and was not, therefore, readily adaptable to conditions soon to be encountered in the Pacific.

No underwater demolition personnel had been trained or were available for the Tarawa operation. However, during the first week of November, 1943, the Fifth Amphibious Force took the first concrete step taken in the Pacific Ocean area toward the organization and training of naval combat demolition personnel. Two important factors compelled this step.

They were:

(A) It was obvious that since some future amphibious operations were to be directed against coral atolls, passage to the beaches involved might have to be secured by demolition personnel trained in marine blasting in coral-choked areas.

(B) Although it was known that the Japanese had never used mines or barricades either as profusely or as cleverly as the Germans, it was not known in what manner, with what obstacles, or to what extent the enemy might employ such devices to prevent or impede future landings.

Once the decision was made the search for personnel began. It was soon discovered that the only individuals who had had experience in marine coral blasting were the Naval Construction Battalion personnel then engaged in coral lagoon clearance projects in various atolls in the Pacific. Some of these officers and men were assembled at Waimanalo, Oahu, T.H., early in November for the purpose of serving as a nucleus to train other personnel in coral work. This modest training program was given terrific impetus by the results of Tarawa.

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 would be necessary for trained personnel to search the water off the beaches to be assaulted for anti-boat mines, tetrahedra and other obstacles, blast and mark channels to such beaches, and otherwise make the passage from ship to shore nearly safe as possible.

At the end of November, 1943, there were approximately thirty officers and one-hundred and fifty men in training in underwater demolition work at Waimanalo. These officers and men were divided into two groups which were called Underwater Demolition Teams #1 and #2. The personnel of these teams, in addition to the Naval Construction Battalion personnel previously mentioned, consisted of Army, Navy and Marine officers and men. Included in the Navy personnel were several Naval Combat Demolition Units which had recently reported from Fort Pierce.

In the latter part of December, 1943, Underwater Demolition Team #2 was ordered to San Diego where it was attached to CTF (Command Task Force) 53 (Rear Admiral Conolly) for use in the attack on Roi-Namur in the Flintlock Operation. Command of this team was given to Lieutenant Commander J.T. Koehler, USNR.

Underwater Demolition Team #1 remained in training at Waimanalo and became a part of CTF 52 (Vice Admiral Turner) for use in the attack against Kwajalein Island in the Flintlock Operation. The officer in charge of this team was Commander E.D. Brewster (CEC), USNR.


As previously indicated, Underwater Demolition Teams #1 and #2 consisted of Army, Navy, and Marine personnel, each team having approximately fourteen officers and seventy men. Efforts to organize the personnel of these teams along both military and operational lines were not entirely satisfactory. Although lack of time was one factor, the main reason was because the teams were composed of small groups of men who had been, for varying periods of time, under the command of certain officers who were also members of the Teams. This made it difficult for these men, as well as for these officers, to adjust themselves to a new chain of command.

In spite of the foregoing, the inclusion of the Teams in the operation was not wholly without profit. Each Team made an extensive pre-assault reconnaissance of enemy beaches and, following the landing of assault troops, blasted channels to the beaches for various types of landing craft and for LST'S. No man-made underwater obstacles or anti-boat mines were encountered by either Team. However, much valuable experience was gained under combat conditions and it was this experience which made possible the organization of the present Teams on a sound basis.

It was discovered in the Flintlock Operation that existing allowance lists of explosives and material would have to undergo radical revision and that, aside from tetrytol, prima cord, composition C-2, steel bangalore torpedoes and sixty per cent gelatin dynamite for post-assault work, no other explosives were necessary. It was also discovered that drone boats, in their then state, were not satisfactory and that extensive changes would be necessary before the use of such boats could be justified. Finally it became clear that, in future operations, each Team should have its own ship in order to avoid the inevitable delays that occur when personnel must be assembled from various vessels prior to engaging in assault operations. Upon the return of Underwater Demolition Team #2 from the combat area, the Commanding Officer of this Team was ordered to prepare a proposed organization plan for future Teams and for a training base. This plan was accordingly prepared by him, was modified in certain particulars by the Gunnery Officers of CinPac and FifthPhibForPac and, so modified, was adopted. The basic letters covering the organization of the training base and of the Teams were issued by the Commander, Fifth Amphibious Force, Pacific Fleet, and were dated 14 March, 1944 (serial 00334 -- C5A/S76/Ply) and 15 March, 1944 (serial 00370--S76/Pl6P).

Experience gained in recent combat operations and in training revealed the need for certain modifications in Team organization. These modifications were embodied in a letter prepared by the Commander Amphibious Forces, U.S. Pacific Fleet. In substance, such modifications provided for the reduction in officer personnel of a Team from sixteen to thirteen, the increase of enlisted personnel from eighty to eighty-five, and the removal of drone personnel as members of a Team.


The use of drone boats fell within the pre-assault demolition phase of operations and was considered at this point. In the Marshall Islands operation, Underwater Demolition Teams #1 and #2 both carried drone LCPR'S. These boats were equipped with hydraulic gear and were controlled by visual observation. Each of the boats was loaded with 6,000 pounds of tetrytol. Although the tactical situation encountered did not require the employment of drones, attempts were made to use them before the assault began. These attempts were unsuccessful partly because sufficient precautions were not taken to protect the transmitters from weather exposure and sea water, and partly because some of the boats were old and in poor mechanical condition. Most of these drones were returned to the Hawaiian Area, were repaired and were made available for the assault on Saipan Island. However, it was again true that the tactical situation encountered did not make the employment of drones necessary and no attempt was made to use them.

When the control vessel was another LCVP, good results were obtained up to 1,000 yards. However, excellent results in controlling drone LCVP's was achieved by carrying control equipment in aircraft. SNB-1 and SBD-1 type aircraft were used as controls and excellent results were obtained in controlling LCVP's singly and in pairs.

During the operations as Roi-Namur in the Flintlock operation, Underwater Demolition Team #2, in bulldozing and loading on coral ledges of an extremely dense nature, used an average of three and one-half pounds of explosives per square foot to remove one-half cubic foot of ledge.

The major task of Teams #1 and #2 after the first assault waves landed consisted of blasting trees and channels to the beaches, the location of such channels having been determined by the information gained during the reconnaissance phase of the operation.

See Page 2, UDT One and UDT Two, for additional team history for those teams.

(compiled by Robert Allan King for the UDT-SEAL Museum from public records at the Operational Archives of the Naval Historical Center)

TEAM ROSTERS - To protect the integrity of the Teams and the privacy of individual frogmen, Team rosters are not made public. If you or your relative was a member of UDT Team One or Two and you would like further information, we suggest you contact the UDT-SEAL Museum.

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