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.
Aluminum Matting Runways in Vietnam
By E. T. Lyons
Twenty-three days after landing at Chu Lai on the coast of Vietnam in May 1965, the Navy Seabees had constructed a runway for the landing of jet fighters. They did this with the aid of a new development in combat airfield paving, aluminum plank matting, commonly known as AM-2. Since then, AM-2 has become almost the standard answer to the problems of airfield construction in Vietnam. Claims for it, concerning the speed of placing and versatility of use, have evoked enthusiastic reception of it under the stress of wartime conditions.
AM-2 consists of extruded aluminum mats or planks that may be interconnected to form an airfield of any size or shape. A full mat is 12 feet long, 2 feet wide, and 1 ½ inches thick. Half mats, 6 by 2 feet, are also used. The material weighs 6 pounds per square foot, or 144 pounds per full mat. It is equipped with connectors on all four sides for joining with other mats. Special mats are available for center line lighting and catapult guide rails. The matting can withstand aircraft landing impacts and jet blasts.
The matting was developed1 as part of an airfield system called “The Short Airfield for Tactical Support (SATS) Concept.” The system involves a short airfield, 2,000 to 3,000 feet long y 72 feet wide, on which a jet aircraft may land by using arresting gear, and take off by using catapults. In the SATS concept, an AM-2 airfield has an expected life of 1,600 cycles of a 27,000-pound single-wheel load with a 400-pound-per-square-inch tire. For this life the matting may be laid on a prepared surface with a CBR of 7-10. For sites where mud pumping poses a potential problem, a lightweight and flexible plastic membrane (vinyl covered nylon) surfacing material may be laid under the matting. This membrane material, weighing 10 ounces per square yard, resists oil, chemicals, and grease, will not support combustion, and resists rot and mildew. Punctures can be permanently mended.
The SATS concept is for tactical operations of thirty days or less, after which the airfield matting is moved forward to a new operational area.
None of the present or planned AM-2 airfields in Vietnam follows the SATS concept. Although the Chu Lai airfield was operated at first as an SATS field, it was designed as a runway 8,000 feet long by 102 feet wide, with taxiways, aprons, and maintenance facilities. A subsequent concrete parallel runway is now under construction. The AM-2 airfields later constructed at Cam Ranh Bay and Phan Rang were planned to be similar to that at Chu Lai except that the runways are 10,000 feet long. Although these runways are called “Expeditionary,” they differ extensively from the SATS concept. They can be considered semipermanent installations. These airfields are in the coastal enclaves controlled by American or South Vietnamese forces. The land routes between them are controlled to a great extent by the Viet Cong, thus making the air transportation of personnel and materials vital to operations. The transport traffic, combined with combat sorties, places a heavy operational load on the runways. Many of the mahor airfields are supporting up to 40,000 cycles per month. So far, traffic on the AM-2 runways has not reached this rate, but it is inevitable that these runways will be loaded to capacity as operations increase.
BASE PREPARATION AT CHU LAI
To increase the potential life of AM-2 airfields, base preparation must be improved. At Chu Lai, the Navy Mobile Constriction Battalion 10 has provided a continuously operational jet airfield and has conducted extensive experimental work for future AM-2 runway base designs. The original operational strip, 3,500 feet long, was laid on a laterite base 10 inches thick. This material is decomposed rock containing iron oxide, and is used extensively in Vietnam for binding sand and for road surface courses. As with any natural material, various grades are to be found. Confined to a small beachhead area, the Seabees had little choice of materials, and the laterite available has provide to be of very poor quality. Although it was originally planned to use the plastic membrane seal between the laterite and the AM-2, the plastic material was not available in time for the first section of runway, This 3,500-foot section, enough for jet operations with JATO take-offs and arresting-gear landings, was therefore laid without a seal under it. It was started on May 7, 1965, and completed in twenty-one days. By July 3, the Seabees had constructed the entire 8,000-foot runway, an 8,000-by-36-foot taxiway, and an operational parking apron of 28,400 square yards. On July 26, the Seabees began to remove the AM-2 on the first section of runway, reshape the laterite, and seal it with bituminous material. Flight operations were not interrupted during this work, and the sealing was completed in August.
During the late summer and continuing through the autumn, the airfield was subjected to torrential rains, and the poor quality laterite base began to fail on the south end in late August. In September the Seabees replaced the south 3,500 feet of laterite base with soil cement, 8 percent by volume, and compacted it with 30-ton oscillating rollers. The soil cement was seal with bituminous materials and topped with a sand blotter. The south end was completed by MCB-10 in December 1965. The next month, the men of MCB-4, which relieved MCB-10, began similar work on the north end and completed it on February 23, 1966. For ten months, while subjected to extreme high temperatures and heavy rainfall, the Seabees had constructed and maintained a jet airfield and had conducted full –scale tests of aluminum matting runways under combat conditions.
USE AT CAM RANH AND PHAN RANG
The second important airfield in Vietnam, constructed of AM-2 matting2, was at the Air Force Base at Cam Ranh Bay. The runway is 10,000 feet long by 102 feet wide. The subgrade at the site is composed entirely of sand. Because of the experience at Chu Lai, particular attention was given to the base under the matting. Extensive soil stabilization work beginning on August 22, 1965, included flooding the sand with sea water and rolling to stabilize it sufficiently to support earthmoving and compaction equipment. Following grading and compaction, the base was sealed with bituminous material. Laying of matting started late in September, and the runway was completed on October 16. With completion of the runway, parallel taxiway, high-speed turnoffs, and 60,000 square yards of operational apron, all in AM-2 plank, the scheduled operational date of November 1 was met. In addition, 132,000 square yards of pierced steel plank apron for propeller aircraft was laid.
Service of the runway has been very satisfactory to date. During heavy rains in December 1965, water stood several inches deep on the runway, but no significant deterioration of the base occurred.
Another AM-2 runway, identical in size to that at Cam Ranh, was constructed at Phan rang. It was started in September 1965 by the 62d Army Engineer Construction Battalion. Once again, the quality of the base has been improved. At this field a graded fill material was placed beneath the matting. For the first time the flexible plastic membrane was used as a seal. The first aircraft was landed on the runway on February 20, 1966. The entire 10,000-by-102-foot runway was completed on March 15, along with sufficient taxiways and aprons to provide an operational jet field.
Although for long-term use the base preparation for AM-2 runways becomes increasingly important, the aluminum matting offers many advantages over Portland cement and bituminous concrete in Vietnam. It eliminates the need for concrete aggregate (which often is not readily accessible to combat airfield sites) as well as the equipment, work, and time required to crush the aggregate, prepare the mix, excavate the foundation, install forms, and place the concrete. Procuring, delivering, and setting up crushing and batching plants in Vietnam may take as long as five months. AM-2 requires only the equipment to deliver the 2,000-pound pallets, and they can be placed entirely by hand, if necessary.
Aluminum matting provides a valuable new tool for the construction of airfields in forward or remote areas. In combat landing operations, this matting makes it possible to construct jet airfields when and where it would otherwise be impossible.
[reprinted from TME / July-August 1966]