TME Looks Back: Vietnam – “Military Geography of Indochina”

This week in TME Looks Back: Vietnam, the subject is geography of Southeast Asia and why…”it is important that the American military engineer visualize and understand the conditions that exist in that region.” Authored by James Reynolds, then a civilian with the Department of Defense and previously an engineer officer with service in Vietnam, “Military Geography of Indochina” was published in the September-October 1965 issue of The Military Engineer.

The article appears below in mobile-friendly format.

In the summer of 2016, SAME will publish a special issue of The Military Engineer commemorating the service and contributions of military engineers in the Vietnam War. As part of the run-up to the publication, over the next several months we will be featuring on Bricks & Clicks a special series entitled TME Looks Back: Vietnam featuring past articles, photos, advertisements, covers, and other material that first appeared in the magazine during the 1960s and early 1970s. [The TME editorial staff welcomes input as we develop the Vietnam Commemorative Issue. Contact TME Editor Stephen Karl at for more information or click here to contribute editorial content. Contact Stephanie Satterfield, SAME Marketing Sales Manager at for sponsorship/advertising inquiries.]



Military Geography of Indochina

By James A. Reynolds




In view of the present situation throughout Indochina and the increased United States involvement there, it is important that the American military engineer visualize and understand the conditions that exist in that region.


Indochina is a geographical term which designates the area of the former colonial territories of French Indochina. It consists of four independent countries: North Vietnam (the Democratic Republic of Vietnam)*, South Vietnam (the Republic of Vietnam), Cambodia, and Laos. Together, these countries occupy about 283,000 square miles, an area about the size of the State of Texas. The population of 39,000,000 comprises—17,000,000 North Vietnamese, 15,000,000 South Vietnamese, 5,000,000 Cambodians, and 2,000,000 Laotians. The population is most heavily concentrated in two regions: the Tonkin delta in the northeast, which contains the cities of Hanoi and Haiphong, and the Mekong delta in the south, which contains Saigon. These are the two most important rice producing areas in Indochina.


The climate is controlled by the prevailing winds and the configuration of the terrain. During summer, May through September, warm moisture-laden winds blow into Asia from the southwest—the southwest monsoon. This brings rain to the slopes facing westward and southwestward. Conversely, in winter, October through March, the monsoon wind is from the northeast, bringing rain to all eastward exposures. Thus, in a country where temperatures are always warm, with mean daily temperatures ranging from 70 to 95 degrees Fahrenheit, the variation in climate is in the timing and amount of rainfall. Local variations in rainfall are great, but usually there are 50 to 115 inches annually. From January through April, the northeast coast is subject to periods of low, dense clouds, fog, and drizzle, known as crachin, which may persist for as long as two to three weeks with few breaks during which the sky is visible. These severely restrict air operations. The eastern coast may be subjected to one or two typhoons each year.



Throughout most of its length, Indochina is divided by the Chaine Annamitique, which forms a major barrier between the coastal plains of Vietnam and the interior plains of Laos and Cambodia. The Chaîne consists of rugged, densely forested mountain and hill ranges, in a northwest-southeast direction with spurs at right angles to the main ridge which break up the valleys between. In northwestern Laos, mountains trend northeast-southwest. Summit elevations are generally between 5,000 and 8,000 feet above sea level, and ridges stand more than 3,000 feet above valley floors. The highest peak, slightly over 10,000 feet, is in northwestern North Vietnam. Extensive areas of karst, extremely dissected limestone ridges and pinnacles, are common throughout the mountains and bordering hills. Through the highlands, streams flow swiftly in deep, narrow channels.

Bordering the hill and mountain areas are the plains: the Tonkin delta in the northeast and the Mekong delta in the south, and along the coast between these two are the coastal plains which are interrupted in places by spurs of the Chaine Annamitique. The plains are low, flat, poorly drained, and intensively planted in wet-land rice. Meandering streams and networks of irrigation and drainage canals lace these areas.

West of the highlands of the Chaîne Annamitique are numerous higher plains or plateaus, such as the Plaine des Jarres in Laos and the Plateau du Kontum in South Vietnam. These elevated plains consist mostly of grass- and scrub-covered rolling terrain with some open forests. Rice and dry crops are cultivated along many of the drainage ways.

To the southwest lies Cambodia, primarily a low flat plain that rarely exceeds 50 feet elevation. A feature which greatly influences life in Cambodia is the Tonle Sap, a shallow lake which overflows during the flood season. From January to June, the lake drains into the Mekong and is normally 100 miles long by 20 miles wide at its widest point and 6 feet deep. Floods in July through September, resulting from the southwest monsoon, reverse the flow from the lake, tripling its size and increasing its depth to 40 feet or more. This alternate filling and draining of the Tonle Sap, with its consequent variations in water surface elevation and extent, greatly affect construction, rice cultivation, and movement around its shores. In southwest Cambodia, a narrow band of partly forested, rugged mountains with broad, rolling summits and steep, severely dissected slopes rise to a height of 5,000 feet.


The ruggedness of the area has restricted its development, limiting overland transportation mainly to the two main river basins and a narrow strip along the east coast. Primary roads, mostly one or two lanes wide, have bituminous-treated or crushed-stone surfaces, and are constructed on an embankment to prevent flooding. Secondary, one-lane roads have earth or gravel surfaces and are subject to frequent flooding or washouts. Bridges on main roads are usually of steel or reinforced concrete; those on secondary roads are mostly timber or light steel. Many of the bridges are narrow and of low capacities, and numerous fords and small ferries exist, some even on main routes.

The rail lines of Indochina, all meter gage, are separated into three national networks—North Vietnam, South Vietnam, and Cambodia. There are no rail lines in Laos. The two Vietnamese systems were joined prior to the war with France, providing service from Saigon to Hanoi, but most of the lines in North Vietnam were destroyed during that war and have never been completely rebuilt. The main line was reopened in mid-1964 as far south as Vinh. Now the rail lines of both North Vietnam and South Vietnam are frequently blocked and destroyed. In South Vietnam, the Communist Viet Cong mine the track and destroy bridges. In North Vietnam, American and South Vietnamese aircraft bomb and destroy railroad bridges. It would be impossible to predict how much or what portion of either rail system will be in operation at a given time. Rail traffic moves across the Communist Chinese border northwest of Hanoi where the Chinese and North Vietnamese rail lines are both meter gage; but at the border northeast of Hanoi, the lines are of differing gage and transloading is necessary.



Navigable inland waterways are important supplements to overland transportation, the Mekong, the Tonle Sap, and the Red River being the principal systems. The mouths of the Mekong, with their interconnecting canals and tributary streams constitute a network of trade routes over which native junks have traveled for centuries. The only two significant ports in these systems, Saigon and Haiphong, are both upstream from the coast line, Saigon being 46 miles inland and Haiphong 16 miles inland. Port facilities at both are adequate for POL storage, warehousing, and docks and berths for local and regional needs.

The relative insecurity of surface travel has added increased importance to the expansion of air travel. Airfields and landing strips of varying sizes have been constructed throughout Indochina. A few are suitable for heavy jet transports. Although most airfields are primarily for military use, civilian air traffic has shown a marked increase over the past few years.


From the standpoint of military operations and logistics, the maneuver and supply of large forces would be severely hampered by the rugged forested mountains, the numerous streams, the extensive rice fields, and lack of an adequate transportation system. Conversely, the terrain is ideally suited for the guerrilla warfare, such as that being conducted by the Communist forces in South Vietnam and Laos. Insurgent forces emerge from hiding to destroy bridges, crater roads, assault a lightly defended outpost, or spring an ambush. Then, before the conventional government forces can react, the insurgents return to the relative security of the dense forests, swamps, or rice fields.”

With the introduction of American ground combat units into South Vietnam, the military engineer is being called upon to counter the combined adverse effects of terrain, climate, and guerrilla activity. He must construct and maintain suitable roads and airfields for logistical support in densely forested mountains and flooded fields. He must insure rapid movement of tactical units across terrain where movement is virtually impossible. He must prepare defensive barriers on terrain that greatly favors the attacking guerrilla forces. The ability of the military engineers to perform these operations will be a major factor in the attaining of peace in Indochina.


[Reprinted from TME / September-October 1965]

*The Democratic Republic of Vietnam has developed from the so called “Viet Minh” communist regime of Ho Chi Minh, sponsored by the U.S.S.R. The rise of the Viet Minh resulted from nationalist opposition to the French colonial authorities who had submitted to Japanese pressure and Vichy authorization to continue administration of the country after the fall of France in 1940. Ho Chi Minh organized the nationalist guerrilla forces to fight the Japanese and the identification of the French colonial authorities with the Japanese military invaders during the period 1940-1945 provided double objectives of hatred for the nascent nationalistic movement. There is a long story behind the political, economic, and social situations associated with the present conflict in Vietnam.