TME Looks Back: Vietnam – “Conglomerate Tactical Bridging”

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In summer 2016, SAME published a special issue of The Military Engineer commemorating the service and contributions of military engineers in the Vietnam War. To accompany the publication, we are featuring on Bricks & Clicks a special series entitled TME Looks Back: Vietnam featuring past articles, photos, and other material that first appeared in the magazine during the 1960s and early 1970s. 

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Conglomerate Tactical Bridging

By Lt. Col. Taylor R. Fulton, Corps of Engineers, United States Army

 

One of the most unusual tactical bridges constructed by American engineers in Vietnam is on the famous coastal highway QL +1 (Street Without Joy) about 10 miles south of Tuy Hoa. This bridge, a combination of two Class 60 floating bridges and one Class 50 fixed span bridge, was constructed across the Ban Thach River at Ban Nham during Operation John Paul Jones in July 1966.

This operation was to be conducted by the 1st Brigade, 101st Airborne Division. Its purpose was to open up the valley south of Tuy Hoa so that rice farmers could return to their land and to secure the Vung Ro (bay) area for development of a new deepwater port to support the military forces in the area. The 39th Engineer Battalion (Combat), reinforced by the 553d Engineer Company (Float Bridge) and the 572d Engineer Company (Light Equipment), was assigned to provide engineer support for the operation and to construct the new port facilities at Vung Ro. The tactical operations required the brigade to sweep south from Tuy Hoa to secure the high ground above Vung Ro so that an engineer amphibious task force could land on the beach. The task force, consisting of Company A, 39th Engineer Battalion, reinforced by elements of Headquarters Company and the 572d Engineer Company (Light Equipment), left Cam Ranh Bay on July 23 aboard the LST Henry County. The 39th Engineer Battalion (reinforced) minus the task force elements had reached the Tuy Hoa area earlier and was preparing to support the drive to the south. The key to the success of the operation was the rapid opening of highway QL +l from Ban Nham south to Vung Ro. The valley area south of Tuy Hoa had been under Viet Cong control for several years. Villages had been destroyed during previous operations and the highway was blocked by numerous ditches cut across the pavement and blown bridges and culverts. Since Operation John Paul Jones was to start on July 23, highway QL #1 should be opened to Vung Ro, at least for light reconnaissance vehicles, by July 25 when the task force was to land. Four major bridges had been destroyed in this stretch of highway, but only air reconnaissance had been possible prior to the start of the operation, and even this had been hazardous. Detailed information concerning the destroyed bridges and the condition or existence of bypasses was, therefore, lacking, so engineer reconnaissance teams had to accompany the infantry in their advance to relay information back to the battalion as quickly as possible.

TME Looks Back: Vietnam


 

 

The line of departure for the combat troops was the river Ban Thach. Although a partly destroyed 850-foot concrete T-beam bridge was standing at Ban Nham, the usable concrete spans were old and damaged and the destroyed spans had been replaced by French Eiffel bridging.1 The piers and superstructure were badly damaged; at best, the bridge might take Class 12 vehicles. And no bypass was possible. It was, therefore, decided to construct a Class 60 float bridge just downstream from the existing bridge. Construction of the tactical bridge was to begin at 6:00 a.m. on July 23 and be completed sometime on July 25 so that heavy engineer equipment could be rushed south to work on bypasses around other destroyed bridges.

This critical and difficult bridge construction task was assigned to Company C, 39th Engineer Battalion, which was supported by the 553d Engineer Company (Float Bridge). Detailed reconnaissance of the bridge site was not permitted prior to the start of the action for fear it might compromise the operation. Even the tactical bridging itself was not available to load and check as in the normal procedure. The bridging was transported on one ship and the bridge company with its equipment on another. The bridging arrived on July 21 and was off-loaded on the Tuy Hoa beach by transportation units. When the bridge company arrived on July 22, it found the bridging literally dumped in a pile on the beach.

Construction of the Ban Thach float bridge can be divided into five phases:

Phase I, Preparation; II, Construction of Class 60 float bridge from the near shore to Sandbar Island; III, Construction of a road across the island ; IV, Construction of Class 60 float bridge from the island to the far shore; V, Maintenance and improvement.

 

PHASE I–PREPARATION FOR CONSTRUCTION

Upon arrival of the 553d Engineer Company at Tuy Hoa South beach on July 22, it off-loaded its engineer equipment and began round-the-clock operations to group the Class 60 bridging into bridge loads. The bridging was loaded during darkness and was convoyed to Company C at the assembly area. During the night of July 23 while the bridge loads were being prepared, the bridge site was reconnoitered to select the bridge center line and the construction sites. Two platoons from Company C loaded some of the Class 60 bridge materials needed for site preparation on their 5-ton dump trucks so that work on the sites could begin at first light the following morning. The bridge center line was sited adjacent to and 20 feet downstream from the damaged Eiffel bridge. But it was necessary to locate the construction sites upstream of the existing bridge because of shallow water and lack of space for construction sites downstream. At this time it was discovered that Class 60 steel treadway end ramp sections were missing and there were not enough bridge pins. Plans were promptly made for expedient construction of end ramps from M4T6 decking.

 

PHASE II—FLOAT BRIDGE, NEAR SHORE TO ISLAND

Construction of the bridge was begun at dawn on July 24. Three work sites were organized: one for building end sections and the other two for building successive bays. Only two cranes were available, so construction was slow. Upon completion of each bay, it was floated downstream under the blown bridge and joined to the floating span. Anchor cables were secured to the existing bridge piers and bridle lines were run to each bay as it was joined. Impeded by shallow water, inadequate space, shortage of equipment, and the varied type of bridging, the construction of the 375-foot east span was not completed until late the first night. Since everything else was so bad, the missing Class 60 end ramps hardly caused a comment. To offset this difficulty, the bearing plates of an M4T6 dry span were welded to the Class 60 treadway. The makeshift end sections were placed early the second morning and a dozer crossed to Sandbar Island.

 

PHASE III—ROAD ACROSS ISLAND

Sandbar Island was an easy obstacle to overcome. Early the second day, a hasty roadway across the island was cut by the dozer and then covered with PSP. This was designed only to support the crossing of the assault elements and to provide a ford if the water level should rise unexpectedly and cover the island. During this phase, work sites were prepared on the island for construction of the span to the far shore.

 

PHASE IV—FLOAT BRIDGE, ISLAND TO FAR SHORE

An unexpected problem arose as soon as this phase began. This channel of the Ban Thach River was too shallow for a 27-foot powerboat and the water adjacent to the construction site was too shallow for the construction of floats. A crane with a clamshell attachment was rushed to the site to dredge and deepen the river. These site preparations used most of the daylight hours. Working into the second night, successive bays and the end sections were constructed and pulled into place by hand. By the morning of July 26, the second set of expedient M4.T6 end sections were in place, and by 11:00 a.m. the bridge was opened to traffic.

Although this project took a day longer to complete than anticipated, the rest of highway QL #1 to Vung Ro was opened rapidly and by the morning of July 27 the first wheeled vehicles reached the high ground west of Vung Ro. The task force had landed as planned on July 25 and was already hard at work turning the jungle into a hardstand for what would soon be the new Port Lane.

 TME Looks Back: Vietnam


 

 

PHASE V–MAINTENANCE AND IMPROVEMENT

Although the bridge was now passable for traffic, it was far from complete and improvements were needed. Responsibility for the bridge maintenance and security was assigned to the Float Bridge Company. First it was necessary to alter the anchor system and to add guy lines from each shore. The upstream guys were mounted on makeshift 55-gallon drum buoys. Since the Ban Thach River is tidal with changing current directions, kedge anchors were attached to every fifth float on the downstream side. Next, consideration had to be given to the approaching monsoon season during which Sandbar Island probably would be flooded with 6 to 8 feet of water, making it unusable as a ford. This condition was remedied by constructing a steel Class 60 treadway fixed span on Class 50 trestles across the island. M4T6 dry spans were again used as ramps to connect the fixed span to the floating Class 60 bridges on both sides of the island. This eliminated the PSP roadway and made it possible to adjust the height of the overland fixed span to the changing flood depths.

Finally, in November, the monsoons came and put this conglomerate bridge to the test. With the water rising over 8 feet above the July stage, the only adjustments required were raising the Class 50 trestles to keep the dry span clear of the flood water, and the extension of the M4T6 end sections to adjust to the increased river width. Both of these operations were conducted whenever river conditions warranted. The work was done usually at night to avoid interruption to traffic.

Trestle sets were needed for other tactical bridging operations, so, after the monsoon season passed, the 553d Engineers began in January 1967 to replace the trestles with timber crib piers. Judging from the experience gained in the 1966-1967 monsoon season, it is believed that the bridge is suitable for continuous operation until it can be replaced by a semipermanent fixed bridge.

Throughout the period of construction and maintenance, beginning in July 1966, the 553d Engineer Company (Float Bridge) provided a 24-hour guard on the bridge to insure continuous security and maintenance, and to report on changing river conditions which could necessitate modification of the bridge. Six separate sniper attacks occurred at the bridge site causing casualties on both sides.

This is a seven-part bridge: M4T6 dry-span end section; Class 60 float bridge; M4T6 dry-span end section; Class 60 dry-span trestle (cribbed); M4T6 dry-span end section; Class 60 float bridge; M4T6 dry-span end section. It forms a vital link in keeping highway QL l open from Cam Ranh Bay to Qui Nhon. Its construction and service have proven the great versatility of bridging equipment available to the United States Army and the ingenuity of engineer units in adapting various types of bridging to the peculiar combat conditions existing in Vietnam.

TME Looks Back: Vietnam


[reprinted from TME / September-October 1967]