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"Combat Demolition Units of the Atlantic Theatre of Operations," n.d. World War II Command File, Shore Establishments, Operational Archives Branch, Naval Historical Center.

  • Theater of Operations--American
Document Type
  • Monograph-Research Report
Wars & Conflicts
  • World War II 1939-1945
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Location of Archival Materials

Demolition Units of the Atlantic Theatre of Operations

This is a brief history of the demolition units which operated in the Atlantic theatre, their early training, their organization after basic training and advanced training, the difficulties they encountered and the ultimate success in accomplishing their mission. Their missions were unique in that they were assault demolition in nature in contrast to the Pacific operations, which were reconnaissance, and pre-assault demolition. Because they were the first demolition units to operate in any theatre, many problems were met and lessons learned which proved helpful in determining training and policy in later operations. For these and many other reasons it will be necessary to go back to the origin of the units, and briefly follow them through the operations of the Atlantic theatre.

The Naval Combat Demolition Unit started in June of 1943 at Fort Pierce, Florida. The first class arrived and assembled for training the first week in July 1943. The personnel were drawn from three sources, primarily because it was reasonably expected that men from the Construction Battalions, the Bomb Disposal School and the Mine Disposal School would already be familiar with explosives and basic demolitions. The site was chosen because it offered natural swimming beaches and desirable temperatures for year round swimming. Too, it was at a base where demolitions could be carried out and problems could be worked out with the rest of the Amphibious Forces that were already in training at the base.

However, conditions were not as desirable there as they appeared. In the first place, there was no training program set up; no one had any idea as to what the mission might be. No one had the slightest knowledge of what sort of obstacles might be encountered, what pattern they might follow or the best method of destroying them, nor the conditions under which demolition personnel might be called on to work. No provisions had been made for the construction of obstacles, supplying of explosives, housing for the men or training facilities for the unit. Clothing, obstacles, training, program, facilities and explosives were therefore non-existent, yet the men were there and the training did go on. Until steps could be taken to get all of these problems settled, the first class spent from eight to twelve hours per day in physical training and rubber boat drill and primacord knot tying. The heat, sand flies and mosquitoes, food and living conditions were intolerable. From this first class came four of the Naval Combat Demolition Units that were the beginning of the demolition force of the Atlantic Theatre. A Naval Combat Demolition Unit was arbitrarily set as one officer and five men, primarily because it was determined in training that the demolition personnel would work as a rubber boat crew and that the number 6 would be the maximum number of men that could be carried in one boat. Training and facilities at Fort Pierce improved by leaps and bounds and consequently the later units which were sent out were very well trained. These better-trained units will be the ones referred to that joined the units in England prior to the landings. All of the units that operated in the Atlantic Theatre were Fort Pierce-trained.

The first unit sent from Fort Pierce arrived in England in November of 1943, and became attached to Commander Naval Forces Europe until such time as they could figure out who they were, what they were sent for and what their job might be. Then, in December, nine more units were sent over. They, too, found considerable difficulty in getting established and were shipped from one end of England to another without finding anyone who had been delegated to the responsibility of housing and training the demolition units. These arrived at Falmouth Corwall England on the evening of 23 December at 2000 and at 0900 they received word that they had the OOD (Officer of the Day) watch for the next seven days and that the men would assume collateral duties as directed by the executive officer. In substance, the memorandum read as follows:

    "1. In addition to your regular duties, you will perform such collateral duties as are assigned you by the executive officer or head of your department.

    2. One of your collateral duties is that of Officer of the Day at King's Hotel according to the following schedule: (This listed seven officers for the next seven days, all of whom were Demolition Officers).

    3. An additional collateral duty is that of hard master according to plan and schedule to be announced by verbal instructions of Officer in Charge."

The first thought of the demolition units after arrival was to set up an advanced training program. While assuming collateral duties, this was a difficult task. But they did fall into the general work of the base, acting as hard masters and watch standers, while assigning the men to various duties about the base. During their spare time, the units kept busy picking up road obstacles, road blocks, concrete masonry, etc., which had been placed as counter-invasion measures at various points along the coast and hauling them to a small, 200-yard wide beach some eight miles from the Unit's offices. There was carried on an abbreviated training program and a beneficial bit of work in demolition.

For advanced training it was felt that additional training was needed in ship salvage, rocket disposal (i.e., for the unexploded rockets which would be found on the beach), mine recognition, and assault demolition practices of the British. Arrangements were made and officers attended these courses and later taught the men. In January, as a result of attendance at the British equivalent of Naval Combat Demolition Unit known as COXE (Combined Operations Experimental Establishment), much intelligence in the form of pictures and literature pertaining to obstacles already placed on the coast of France was obtained. Of all the obstacles mentioned, the high priority was placed on Element "C" or Belgian Gate. This obstacle is a lattice-faced steel gate propped up on the landward side by steel bracings which are fourteen feet long. The face of the obstacle is 10 feet high and 10 feet wide and the whole structure is of six inch angle iron, one half inch in thickness, welded and bolted together and having a gross weight of about three tons. It could easily be rolled onto the beach at low tide and was strong enough to withstand any surf action. Large numbers had been discovered in back of the dune line along the entire coast of France and it was expected that these might be quickly placed on the beaches at a later date. Inasmuch as this was an entirely new obstacle to the Naval Combat Demolition Units, considerable time had been spent in the determination of the best methods for its destruction.

After considerable difficulty in procurement of a priority for steel, two bays of Element "C" were constructed and placed on the aforesaid abbreviated beach. It was found by experimentation on these that the best method of destruction would be by the use of charges - 16 of them placed at sixteen vital points of the structure - which upon detonation would completely collapse the structure and leave no part of it extending above the surface of the beach more than six inches. This proved very successful in the few tests that were permitted. The greatest difficulty in the process came in the attachment of the charges. From this difficulty came research and design of the Hagensen Pack, a small canvas sack, filled with 2 pounds of C2, which could be fitted and secured to the angle iron regardless of its size or shape by means of a line and V-slot hook of special design. Further and complete experimentation by the group on this obstacle was interrupted when orders from higher authority came and split the units into three separate groups. One group departed for Fowey, Devon England to join the Second Beach Battalion; the second group went to the Sixth Beach Battalion at Swansea, Wales and the third group to the Seventh Beach Battalion at Salcombe, Devon, England. Each of these groups continued training on obstacles of any sort when they were available and when satisfactory beaches could be found. The group at Fowey continued research on the Hagensen pack to determine its sensitivity, shrapnel effect, cutting effect and stability, and investigated manufacturing facilities in the event it would be adopted as a standard explosive for the Naval Combat Demolition Units.

The group with the Sixth Battalion located at Swansea, Wales was able to resurrect road blocks, posts and rails and place them on the long flat beaches and practice dry-runs and time trials which later provided important information for the writing of the operational plan. Meanwhile, eight more Naval Combat Demolition Units arrived from the United States to supplement the units already in training. These were divided among the three groups.

By March the 25th of 1943, the Beach Battalions were ready to go to the marshalling area to await orders to invade. In the absence of official word as to what part the Naval Combat Demolition Units would play and what craft would be assigned if they were to be used, it was found necessary to submit to higher authority a letter stating the capabilities of the enemy to place obstacles on the beach in a comparatively short time and the capabilities of the Naval Combat Demolition Units to destroy them either by daylight assault or night pre-invasion demolition. This letter, together with information of the tremendous increase in obstacles appearing on the beaches of France led to immediate action by higher authority to consolidate the units once more and establish a unified plan of attack.

When it was determined that there would be increasingly larger numbers of obstacles placed, that there was a 25 foot tide change twice a day (which meant working in a tide that rose approximately 1 foot every eight minutes) and that the method of attack would involve assault demolition, it became necessary to reinforce the Naval Combat Demolition Units. Fort Pierce had sent all available units, a total of sixteen Naval Combat Demolitions to England by plane, depleting its supply. Personnel from three Army Combat Engineers were therefore assigned for training by the Naval Combat Demolition Units and all gathered at Appledore, England, where model obstacles were being placed on the beaches for assault and demolition practice. The program for the first time was designed specifically to prepare the men and officers for the landings and emphasized the techniques suggested and agreed upon the operational plans by both the Army and Navy which had been submitted to higher authority for approval. The program was hurriedly organized but was excellently planned. Large areas of beach had obstacles, but there was a definite lack of such obstacles as Element "C", Tetrahedrons and hedgehogs, the three obstacles which were known to exist on the beaches. Those that were placed were made of wood and a very poor substitute, yet the placement of the charges was the important practice that could be had.

The training program at Appledore, England got underway on the 15th of April and ended on the 22nd or 23rd of May. During this time the group maintained the three separate group divisions and worked together; two of these were designated as Force "C" and one as Force "U", the designations of the beaches that were to be assaulted. Each group consisted of 11 gap assault teams. Each team was made up of thirteen men; five Navy Naval Combat Demolition Unit men plus five Army men, plus three seamen sent from a pool in Scotland. Each of these groups was backed up by 26 army men who were to reinforce or support the assault group in later clearance of the beach, the entire group being a gap assault team.

During the early stages of the training program, the officers of each of the Naval Combat Demolition Units were taking care of their units, procuring equipment and organizing the men. There was noticeable need for a commanding officer or a senior officer with the power to make decisions or with authority to procure necessary items or determine policy. When a commanding officer was requested, two Lieutenant Commanders were sent from the United States to take command of the units. Their previous experience in demolition work had been a two-week training course at Fort Pierce, just prior to coming over. There was very little time for them to become familiar with the problems and make the proper decisions, but ever so much was accomplished by their presence in obtaining the latest intelligence data and fitting the units into the invasion plan.

After the training program, all units were removed to Salcombe, Devon, England, including the Army men who were temporarily assigned to the Navy for this operation. At Salcombe, most of the time was spent in preparing 10,000 Hagensen C-2 packs, procuring gear and making final preparations.

For the first time, the intelligence information was coming to the units from naval sources. New obstacles, new patterns of placement, and ever increasing numbers of obstacles were being reported, as was predicted by the Naval Combat Demolition Units. By this time, however, it was too late to change plans or to give special training.

Repeated attempts to procure transportation via LST or the equivalent for personnel and the tremendous amount of explosives at this late date failed to produce results except for the Force "U". All such ships were already assigned. Too, it was impossible to procure the use of LCVP's or the equivalent. The only boats available were the LCT(A)'s or LCT's and those were already assigned to transport troops and equipment. But the teams were assigned as additional load to these and plans began for loading and moving to the French coast. One group, the Force "U" which was to assault UTAH beach did manage to get the use of LCVP's for D-Day.

On 1 June 1944, Group 3, the group which was to attack on UTAH beach, left Salcombe for the marshalling area. On 3 June, the remaining Naval Combat Demolition Units, those who were to attack OMAHA beach, left for Portland, England for embarkation.

The operational plans submitted 31 May 1944, and the one rightfully assumed to be followed, called for the departure from the United Kingdom with one gap assault team per LCT(A). (This is the group of 13 men, 1 officer and 26 additional Army personnel in reserve). Sixteen such gap assault teams went aboard the PRINCESS MAUD, a British liner. Loading of the personnel started at one o'clock the next morning. Each LCT(A) had 52 men and 3 medium tanks aboard. The additional men were the crew personnel for the tanks that were being carried and, according to the operational plan, were to land and assist the demolition units by giving support and removing any obstacles not cleared in the initial assault. On 5 June, the officers of the OMAHA force were picked up from the LCT(A)'s and taken aboard the U.S.S. ANCON, the flagship, and there received their first and final briefing. Although this was almost entirely unsatisfactory it did give the men a picture of what was going to happen. The Army personnel aboard the LCT(A)'s were able to give some additional information on intelligence data because they had been in a marshalling area for weeks and were presented with all the available information for perusal and study. Prior to departure and after the officers returned from the ANCON, an LCM was assigned to each LCT(A) and was to be towed to the transport area where the Demolition gap team would disembark onto them and proceed to the beach.


The plan called for the sixteen gap assault teams to land at H-hour plus three minutes, each clear an initial 50 yard gap, (each gap was 200 yards from the adjacent one), widen and extend the gap until it was continuous along the beach or joined the other gap. This gap was to be clear from low tide up to the high tide mark, or roughly would be a gap fifty yards wide and 400 yards in depth. If the seaward band of the obstacles were Element "C", ten of the support team personnel were to assist the Naval Combat Demolition Unit Army gap assault team in the placement of the charges. The remaining personnel were to continue to the succeeding bands and begin clearance. When the tide, which was at low ebb and just on the rise, necessitated stoppage of the work, a green buoy was to be placed at the flanks of the gap thus far cleared and two range markers of different lengths were to be placed at the dune line in the center of the gaps so that ships could be guided into the beach through the cleared gap. This method of gap marking was inadequate but was a task which the gap assault teams had to assume prior to leaving the United Kingdom when no definite decision was made or direct assignment given to have the gaps marked after they were blown. The sixteen teams were to land as a wave, load the obstacles with explosives, mark the gap extremities, and fire at will (but with a purple smoke signal to indicate pulling of the fuse-lighter), and return inland across the beach as far as the two-minute fuses would permit and take cover in any manner possible. As the tide receded the units were there to clear the remaining obstacles those not removed on the initial assault and continue working until the entire beach was cleared.

Preliminaries to the assault were to be as follows: there were to be a total of 1000 to 1500 planes passing continuously over the convoy en route to France. These would continue to their objectives, the communications lines, the railroads, the bridges, the roads, etc., deep inland from the beach. These planes were to keep a continuous bombardment for twenty-four hours prior to H-hour.

Naval gunfire from Battleships, Cruisers, and Destroyers was to begin an hour or so before H-hour, which was to be at 6:30, at which time it was to be lifted to objectives above and beyond the beach. Nine LCT(R)'s (Landing Craft Tank-Rockets) each carrying 1050 five inch British rockets were to saturate specific objectives on OMAHA beach and beyond the beach at H-hour minus 15 minutes. At approximately this same time, 32 DD tanks, regular medium tanks with a collapsible canvas tub built around them to permit flotation, sixteen to each half of OMAHA beach, were to be off-loaded at about 500 yards and make their way into the beach firing at definite objectives and targets of opportunity. Three hundred planes were to pass over the beach in waves and drop their bombs in strings starting the first at the water's edge up into the hill behind the dune line. This was to be done prior to H-hour for at that time there were to be two divisions of assault infantry landing to silence any small arms fire that might remain after this saturation of defenses. The gap assault teams, accompanied by two tanks and one tank dozer per gap (a tank with a special blade attached to the front of it) were to touch down at H-hour plus three minutes, begin placing charges and complete their mission of clearing the fifty yard gaps in twenty minutes. The tide was to be at low ebb and just beginning to rise.

The plan as set forth in all probability would have worked out successfully provided the timing of support for the demolition units could have been followed. The original plan left no alternative in case conditions of weather and sea slowed the operation.

Actually, what happened is as follows; the LCT(A)'s having the preloaded LCM's in tow and the demolition gap assault teams aboard started crossing the channel. During the previous 24 hours, the weather had been excellent and the sea smooth; the weather now had taken a change for the worse and the first five hours at sea were extremely rough prompting the supreme Commander to order, at midnight of the 5th of June, a postponement of the operation for 24 hours. All ships had to return via the same rough route to their original berths and await further orders. This forced the personnel to suffer an extremely wet and cold ride of several hundred miles. Conditions aboard the LCT(A)'s were definitely poor; berthing and food facilities were inadequate and almost impossible, with the men forced to sleep on decks which were for the most part awash; one small stove and the utensils were inadequate to prepare the food for the men. Conditions were crowded and the sea was still extremely rough, as the LCT(A)'s got underway for the second attempt to cross the channel. The LCM's began breaking loose from the LCT(A)'s and others were breaking down and being lost completely. The LCT(A)'s themselves in many cases were breaking down or sinking on the way over. Many got lost in the convoy of thousands of ships and on several occasions, Naval Combat Demolition Units had to abandon the LCT(A)'s and board the LCM's and continue under their own power the rest of the way with the convoy to the transport area this completely without food or shelter from the raging sea. Considerable difficulty was encountered in finding the rendezvous area prior to the departure from the transport area once it was reached. The LCM's destined to pick up the support units on the PRINCESS MAUD, found considerable difficulty in locating her to off-load the personnel. At this stage of the operation the personnel were cold, wet and seasick and obviously were not in the best physical condition to carry out their mission.

In spite of all these difficulties, the gap assault teams had an orderly departure from the transport area (this all being done without radio communication, as radio silence was to be maintained until H-hour), and touched down almost in a perfect wave at 0633 to 0635.

Almost without exception every LCM was subjected to mortar, machine gun and French "88" barrages, as the ramp was dropped. Those who were fortunate enough to get off without being hit started to work immediately. It was clear that saturation of the beaches by low flying bombers had not been accomplished on the beach or above the dune line. No planes were seen going overhead nor were bomb craters found on the beach in which Naval Combat Demolition Units could seek shelter from their demolitions. There was Naval Gunfire on the pillboxes, but due to the particular angle of placement of these pillboxes at there opening, the gunfire was rather ineffective. The massiveness of the pillboxes gave adequate protection to the defending gun crews, who continually harassed and fired on the demolition units as they frantically pressed on their work. There was no evidence of unexploded rockets on the beach as were expected. Inasmuch as the LCT(R)'s objectives were not clearly defined to the demolition parties, they may have had objectives inland somewhere. At any rate, the LCT(R)'s added little toward neutralizing the small arms fire of the enemy entrenched along the beach who were hindering the Naval Combat Demolition Units. Only three or four of the 32 DD Tanks were seen in operation, and these were seen in flames shortly after they left the beach to go over the dune line. There were only six of the forty-eight medium tanks operating; the others were either knocked out or blown up so added no assistance to the Naval Combat Demolition Units. The infantry waves which were to proceed the demolition party were arriving and tripping through the primacord ring mains or taking cover behind the obstacles making it impossible for the charges to be fired. Meanwhile, the Naval Combat Demolition Units were under devastating enfilade fire losing personnel by the score, but carrying on the best of their ability.

The obstacles encountered were in three bands with three rows of obstacles per band, in a somewhat consistent pattern, staggered and on ten to fifteen foot centers. They extended from low tide to high tide extremities and were completely dry when work began. A most difficult gap area had several bays of element "C" joined together or staggered, several rows of wooden ramps constructed of 10 inch timber firmly jetted into the ground and reaching a height of nine feet; post tetrahedrons of both concrete and steel construction, and hedgehogs six feet in height of six inch angle-iron one-half inch in thickness, welded and bolted together.

The least difficult gap area had the wooden ramps, stakes, rails and hedgehogs in that order from seaward. All of the obstacles had Teller Mines (42), box mines or anti-boat mines attached. These contained only a pressure device and were primarily meant to blow up the landing craft as they attempted to ram through the obstacles. The gaps which were not completed, or which were not adequately marked soon became filled with landing craft LCM's, LCT's and LCI(I)'s all with gaping holes in the bulkheads. 

In spite of the extreme difficulties, depleted personnel and powder, the demolition units were able to clear eight complete gaps and two partial gaps, all of which were clearly marked and capable of receiving the succeeding waves bringing personnel and equipment.

The method of clearance on the assault phase accomplished by the use of the two-pound Hagensen pack. Each man was carrying about twenty of these two pound charges, safety fuse and detonator assemblies, and continued working until the rising tide prevented further clearance. Post assault clearance, i.e. after the tide receded, was accomplished with tank dozers, caterpillar tractors, and salvage explosives. The mechanical equipment used was commandeered from the Rhino (Pontoon) Barges and any other available sources. The Construction Battalion training which the Naval Combat Demolition Units had had previously was of inestimable value in this work. Removal of wrecked LCM's and LCVP's was accomplished by the use of explosive hose and fifty-pound charges placed in the engine rooms and detonated by electric firing. Complete clearance of the beach was attained by D-day plus two on OMAHA beach.

Casualties on the OMAHA beach for Demolition personnel were 41 percent; 30 percent of the right flank group and 50 percent of the left flank group. All casualties were the result of enemy action and no casualties resulted from improper handling of explosives.


With the exception of the training period at Fowey, England at Pentowain Sands, the advanced training activities of Force "U" parallels that of Force "O". Therefore, It will be well to mention only this portion of the advanced training then pick up again where the groups split at Salcombe, England for the actual assault of the French coast.

At Fowey, the group worked for a period of six weeks, with the 531st Engineers, who had seen combat in Sicily and Salerno. Of particular interest to both the Army and Navy was the Element "C" or Belgian Gate. As was previously mentioned, considerable work and experimentation was made with the Hagensen (C-2 filled canvas sack) pack by this group. All of the tests made were extensive and severe yet the charge proved itself as being very reliable. It got maximum power out of the explosive because it could be placed so closely to the object being blasted, and had far less shrapnel effect. Further experimentation was carried on using this same charge on concrete, and reinforced concrete objects, and on barbed wire. With such successes with the charge, it became advisable to adopt it as one of the standard charges in Demolition. After adoption however, it was necessary to get the charges produced in large quantities. The tremendous shortage of material and labor in the United Kingdom made it necessary to have them made at several different places with the net result that a uniform product was not always guaranteed. This led to the theory that it would be better to have only parts, that is the hook and canvas sacks, made and then to have the demolition personnel assemble and complete the packs themselves. This was done at Salcombe, England and all of it just prior to going across the Channel.

On June the 1st, this group left Salcombe, England for the marshalling area and for the next three days briefing for the operation took place. Maps, plans, photographs, etc., of the obstacles and defense situations were studied and explained to the officers and men of the force. On June the 3rd this group embarked on LST's and moved in the huge convoy of several thousand craft across the choppy Channel to the transport area, arriving at 0300 the morning of D-day with ample time to off-load the personnel and rendezvous properly before moving into the beach in a well-organized wave. Essentially, the bombardment plan was the same as that for OMAHA beach prior to H-hour, with the important exception that the Naval gunfire would not be lifted by a predetermined time but by signal set up on the beach telling them to do so. In this way, the assault infantry were able to gather their forces along the 9 to 12 foot seawall and charge en masse over the wall to silence enemy small arms fire without fear of being hit by their own Naval fire. Too, with the fire power on the defenses until they had gathered and got ready they would have little trouble overpowering any resistance that might develop. The actual assault plan was approximately as follows: at H-hour, which was also 0630, the first wave of infantry would come across the beach and assemble at the seawall and await the signal for the gunfire to be lifted and for them to charge over the wall. At 0635 another wave of infantry was to join them and with this wave was to come the Naval Combat Demolition Units. The Naval Combat Demolition Units were to start work immediately and clear the fifty-yard gaps through the obstacles. All went as planned and the Naval Combat Demolition Units effectively cleared all of their gaps. At H-plus 12 the tanks and tank dozers came in and assisted the demolition units in completely clearing the beach. The personnel of the Army Engineers came in to lend assistance to the Naval Combat Demolition Units at H plus 19 minutes or join with the infantry, whichever was necessary at that time.

By H plus 2 hours, an incredibly short time for such a task, the Naval Combat Demolition Units had joined their gaps so that there was a cleared frontage of over 700 yards though which the subsequent waves could off-load their personnel and supplies. The extremities were clearly marked until receding tide when demolitions were completed and no obstacle remained after the first day.

Obstacles encountered were scattered wooden ramps, eight unconnected bays or sections of element "C", reinforced concrete posts, concrete tetrahedrons and wooden posts. No mines were encountered in connection with the beach obstacles. All obstacles were high and dry on arrival. The intensity of enemy gunfire was not as severe as that of OMAHA beach nor were the obstacles so thickly patterned. The timing and execution of the operational plans were much better, which accounts for better results. In spite of shellfire from rockets, machine guns and "88"s, all hands worked rapidly disregarding personal safety to complete their mission.

The essential difference in actual demolition operations was in the fact that electric firing was used instead of safety fuse, giving much better control in removal of the obstacles. The fact that the men had a more pleasant trip across via LST and the fact that they operated in faster, more maneuverable LCVP's probably added to the efficiency with which they completed their task. Casualties for the Demolition Gap Assault teams on UTAH beach were six dead and eleven wounded. All were the result of enemy action and not as a result of improper handling of explosives.


Published: Tue Mar 20 09:57:59 EDT 2018