The Monsoon War: Weather, Insects, and Animals in the Vietnam War

In the 1960s and early 1970s, Indochina’s weather, insects, and animals posed serious problems for American troops deployed across South Vietnam.

South Vietnam’s heat plagued the Americans. During the dry season, which lasts from early February to the end of April, daytime temperatures along the south-central coast, in the lowlands around Saigon, and across the Mekong Delta regularly rose into the 90s Fahrenheit. American troops, who had been acclimatized to the temperate climate of North America, had difficulty patrolling in such extreme heat. Heavy cotton fatigues (issued in the early years of the war), cumbersome rucksacks, steel-plated flak jackets, and steel helmets only worsened the effects of the heat. Under South Vietnam’s unbearable mid-day sun, GIs became lethargic and dangerously overheated. Trooper Bill Brocksieker remembered his unit’s first month in-country, “We didn’t have no jungle boots or no utilities. Everybody, we drank a lot of water. We were dehydrated easy trying to get adjusted to the heat, a lot of people fainting, a lot of confusion that first thirty days or so.”[1]

High temperatures induced fatigue, which muddled a man’s thoughts and made him more prone to mistakes. Dehydration and heat stroke became serious problems. A Marine stationed in the northern provinces of South Vietnam recalled the effects of heat and dehydration on the men of his battalion. “The mercury level might be 98 degrees one day, 110 the next, 105 the day after that; but these numbers can no more express the intensity of that heat than the reading on a barometer can express the destructive power of a typhoon. The only valid measurement was what the heat could do to a man, and what it could do to him was simple: it could kill him, bake his brains, or wring sweat out of him until he dropped from exhaustion.”[2]

On June 19, 1966, journalist S.L.A. Marshall trudged along on a search and destroy operation with the Marines in I Corps. Two battalions of Marines, 1,800 men, were trying to find and destroy a Vietcong battalion known to be operating in the coastal lowlands. The grunts never found the Vietcong, but they suffered thirty-seven casualties that day, all of them from the heat.[3]

And the Marines continued to suffer losses to the heat, even after having had two years to become familiar with the country’s challenging climate. On April 22, 1967, the Marines launched Operation Beacon Star in the paddy lands of Thua Thien and Quang Tri provinces. In the first three hours of that search and destroy mission, the Marines lost sixty men to heat stroke and heat exhaustion.

High temperatures and humidity caused problems for the U.S.’s helicopter fleet. Humid, warm air did not always provide the necessary lift required by helicopters. A U.S. pilot explained the phenomenon, “All helicopters can lift more when the air is colder and drier and thus denser…In Vietnam, the tropical heat and humidity reduces the maximum safe capacity to six troops with packs. Any more than six or seven can be a real problem.”[4] S.L.A. Marshall saw the effects of high temperatures on U.S. helicopters while on an operation in the Central Highlands, “…because of the altitude density and extreme heat, the choppers, on getting to the clearing [landing zone], found that they could not hover.”[5] As a result, the pilots had to land their birds, which made them more vulnerable to Vietcong ground fire. Although top U.S. military officials spoke repeatedly of the U.S.’s vaunted air mobility, South Vietnam’s climate put limits on it.

During the southwestern monsoon, which runs from May through October, it rained almost every day. And since South Vietnam sits squarely in the tropical climate zone – it rained a lot. Saigon annually receives an average of 51.2 inches of rain. The bulk of that rain falls at the height of the southwest monsoon in June, July, and August. Pleiku, in the Central Highlands, receives an average of 51.9 inches of rain a year. Like Saigon, Pleiku’s highest monthly rainfall totals occur between June and August. Quang Tri, along the northern coastal plain, gets 63.6 inches, or over five feet, of rainfall a year. Most of Quang Tri’s rainfall arrives with the northeast monsoon between September and November. Of course, the above statistics are only averages. Some years recorded far more rainfall.

The United States conducted a cloud-seeding program throughout the years of peak U.S. military involvement in Vietnam. This program probably contributed to record-breaking rains in certain areas of South Vietnam. The architects of the cloud-seeding program hoped that increased rainfall would slow or stop Communist traffic on the Ho Chi Minh Trail. But the clouds seeded over Laos often floated into South Vietnam, where they likely produced historic rain events. Neither the U.S. government nor the scientific community has verified that the cloud-seeding program actually increased rainfall amounts across Indochina. Nonetheless, several freak rain events occurred in South Vietnam during the years of the program.

In the second week of October 1968, U.S. military meteorologists predicted two inches of rain for the Danang area. To their surprise, 36.67 inches fell that week. A year later, on October 5, 1969, Hue recorded its highest single day rainfall total – 22 inches of rain in 24 hours. During the week of October 1-9, 1969, Hue sank under 59 inches of rain. A U.S. weatherman stated that that amount of precipitation was, “greater than any monthly total ever recorded over the past 30 years at any station in Vietnam.”[6] In 1971, the area around Quang Tri City suffered severe flooding – the result of another series of record-breaking rains. Not coincidentally, the cloud-seeding program reached its zenith in 1971, when American planes flew 333 missions over Laos.[7] How many major rain events in South Vietnam between 1965 and the early 1970s can be attributed to the cloud-seeding program may never be known. But the Americans, through the program, may have inadvertently harmed their own military efforts by soaking the South Vietnamese countryside with an abnormal amount of rainfall.

Heavy rains turned much of South Vietnam into a mud hole. During Vietnam’s two monsoon seasons, America’s logistical bases, fire support bases, and night defensive positions became bogs. No one escaped the mud and grime – it pulled at combat boots, caused jeeps and trucks to shimmy and slide off unpaved roads, and stopped big tanks and armored personnel carriers dead in their tracks. Rain, low clouds, and lightning grounded helicopters and jet bombers. Torrential downpours and high river levels slowed or stalled resupply convoys and kept troops from crossing the countryside. During the monsoon, the land reached up with muddy tentacles and held firm to the legs of the American expeditionary force; denying the Americans the mobility they needed to find and destroy the Vietcong. Rain certainly slowed Communist troops marching south along the Ho Chi Minh Trail, but it did the same to U.S. troops stationed across South Vietnam, which meant it lengthened the war and contributed to the Communist’s protracted war strategy.[8]

The rains, and the stagnant pools left in their wake, brought mosquitoes. The tiny insects ravaged the Americans sent into the bush. Marine Lieutenant Philip Caputo remembered a night on the perimeter around the Danang airbase, “Our toughest battle that night was waged against Vietnam’s insect life. Mosquito netting and repellents proved ineffective against the hordes of flying, creeping, crawling, buzzing, biting things that descended on us. From every hooch came the sounds of slaps and cries of “goddamn little bastards, get outta here.” By midnight, my face and hands were masses of welts.”[9]

Mosquitoes carried malaria; the most common of South Vietnam’s many diseases. Although the U.S. military dispensed quinine to the troops, not every GI took the prescribed dose. The drug’s unpleasant taste, along with the requirements of combat, made it hard for grunts in the bush to take the daily dosage. As a result, tens of thousands of GIs contracted malaria during the course of the war. The loss of troops to this disease seriously reduced U.S. combat strength. Marine Lieutenant Bill Masciangelo recounted, “As spring became summer, a serious problem arose with malaria. Between June and September, when the battalion moved to Cam Lo, 206 of its members contracted the disease. Many others came down with FUO, fever of unknown origin. There were times when this and other diseases removed more Marines from the ranks of the able-bodied than did the enemy.”[10] In 1966, S.L.A. Marshall wrote of an American unit that had suffered a fifty percent reduction in manpower because of malaria.[11] Lieutenant Colonel Hal Moore, of the 1st Battalion, 7th Cavalry, 1st Cavalry Division remembered, “…we began losing men to malaria within two or three weeks [of our arrival in South Vietnam]. Within six weeks fifty-six troopers from my battalion alone had been evacuated to hospitals, suffering serious cases of malaria. The problem was a particularly virulent falciparum strain of the disease, prevalent in the Central Highlands; it was resistant to the antimalarial drugs available to us at that time.”[12]

Malaria was only one of many diseases prevalent in South Vietnam. The country was rife with disease. One medical doctor referred to the Mekong Delta as a petri dish – a place that bred infectious diseases. Waterborne diseases thrived in South Vietnam, especially dysentery. Sadly, the South Vietnamese peasantry didn’t help the situation. They often defecated and urinated into streams, rivers, ponds, and paddies; or they threw dead animals and animal parts into waterways. Typhoid, cholera, Japanese encephalitis, and blackwater fever swept across the land, a silent menace passing through U.S. ranks.

Since GIs spent so much time wading through paddies, soaked by rains, or sleeping on the muddy ground, immersion foot (also known as trench foot) reached epidemic proportions. Infantryman C.W. Bowman related the following, “You couldn’t work out in the paddies more than three or four days before your feet would start rotting. There was trench foot, and guys couldn’t walk because of the plantar warts on their feet. Most of us had immersion foot, ringworms, leech bites, and hepatitis.”[13] Added to this nasty mix of afflictions were a host of critters, both large and small, that could inflict injury or death. Leeches were ubiquitous in South Vietnam. Infantrymen on patrol could not avoid the black, slimy bloodsuckers, which drifted down rivers and canals, swam in the muddy water of rice paddies, and hung onto branches, leaves, and blades of grass.

Wild tigers and leopards inhabited the jungles of South Vietnam. Large cats occasionally attacked soldiers, but the number of incidents was low. Marine Lee Ashburn recalled two such encounters, “One of the more bizarre episodes of the war involved wildlife and 3/3 [U.S. Marines]. In April 1967, Corporal David Schwirian, a squad leader from Captain Ripley’s Lima Company, was manning an ambush site north of Route 9 in the middle of the night when a large tiger pounced on him. The big cat pinned the corporal’s weapon hand to the ground by standing on it and began tearing big chunks of flesh from his other arm and shoulder…The wound was serious enough to end Corporal Schwirian’s tour in Vietnam. The tiger escaped and it, or one like it, claimed another victim about a year later, when a Marine from another battalion was killed by a tiger within a few hundred meters of the spot where Corporal Schwirian had been attacked.”[14]

Corporal Kevin Macauley, 3rd Recon Battalion, U.S. Marines, who spent a lot of time in the jungle on stealthy reconnaissance missions, encountered a number of large mammals during his tour of duty. “The animals out there were just absolutely amazing. One patrol, we were waiting for the helicopters to pick us up and an eight-and-a-half-foot-long Bengal tiger came out in front of us, not more than six feet away. I had a rifle ready to shoot it in case it jumped at us and I was aiming all over the sky, I was so nervous. Another occasion we had elephants in the area. We had apes.”[15]

Biologists believe that during the war years, Vietnam’s tiger population may have actually expanded because of an increase in available food derived from the large number of Communist dead strewn across the Central Highlands. It was also possible that the tigers simply became more visible during the war years because they had become habituated to the presence of humans in the jungle, which made them less shy and more likely to prey on homo sapiens.

Vietnam’s poisonous snakes occasionally injured and infrequently killed American soldiers. South Vietnam possessed a sizable venomous snake population, which included the bamboo viper, Malayan pit viper, red headed krait, banded krait, many banded krait, blue krait, and cobra. U.S. troops referred to the bamboo viper as a “two step Charlie” because after being bitten by one, the unlucky GI supposedly took two steps and then fell over dead. In truth, Vietnam’s snakes are not that venomous. A stricken trooper did not die after two steps. However, if a snake bite went untreated, a GI did have a greater risk of infection and death.[16]

Rats were common in rural South Vietnam. Their population increased noticeably during the war years. Base building, pollution, and rapid, unplanned urbanization led to a boom in rat numbers. U.S. hilltop bases, with their earthworks, odd smells, and garbage, acted as rat magnets, drawing the creatures in from adjacent forests, rice paddies, and refugee shantytowns. Out in the bush, American troops generated colossal amounts of garbage, including discarded candy wrappers and uneaten food. This edible refuse fed a burgeoning rat population. Underground bunkers, foxholes, and trenches provided rats with ready-made habitat.

In 1968, the Marines claimed that the North Vietnamese encircled and laid siege to the U.S. base at Khe Sanh. That assertion has long been contentious. But one thing is certain, rats did lay siege to the base. The rodents were everywhere, gnawing their way into food stores, burrowing down into trenches, and rummaging through the underground living quarters of the Marines. Corpsman David Johnson, based at Khe Sanh in early 1968, recalled, “We had a lot of people get bit by rats. They were just thick. The first night we were in the holes up there, I remember we were laying there and there was incoming artillery that was coming over the top of us so you didn’t dare stand or anything. And you could hear them coming down the tracks. You know, just a little pitter-patter of feet. I bet there were seventy-five rats that just ran right across you. Just, zoom.”[17]

Many U.S. soldiers noted the large size of the rats in South Vietnam, believing they became so big because they fed on the flotsam of war. As a matter of fact, Vietnam has a large native rodent known as the hoary bamboo rat. It weighs up to nine pounds and grows as long as 20 inches. In the dark of a bunker in the Vietnamese bush in the middle of the night it looked a lot bigger. The hoary bamboo rat normally lives in the forest, quietly feeding on grasses, leaves, and roots, but disturbances to its habitat brought it onto U.S. bases. American built bunkers provided the big rat warmer, drier, more comfortable accommodations than its own primitive burrow.

The smaller Norway rat also roamed across South Vietnam. It came to South Vietnam centuries earlier aboard European trading vessels. The Norway rat, along with the rice field rat and the Asian house rat, are omnivorous, meaning they can feed on everything from a Sneakers bar to Spam. Not surprisingly, those three species experienced a population explosion during the war.

We know rats spread disease, including the deadly bubonic plague. But more often than not, the critters merely disturbed a grunt’s precious sleep, despoiled food stocks, and burrowed into ditty bags.

To weary grunts, confronted daily by a hostile landscape, it sometimes seemed as though even the pets and farm animals of South Vietnam considered the Americans as enemies. Reporter John Laurence remembered saving a stray kitten he found hungry and scared on the streets of Hue during the Tet Offensive. This cat, although “saved” by a well-meaning American, never took a liking to his “owner.” After years of comfortable living in New York City as Laurence’s “pet,” the cat still ambushed Laurence when he happened to get up from his bed in the middle of the night to go to the bathroom. Laurence eventually realized that the “Cat from Hue” was probably a Vietcong sympathizer, if not solidly Vietcong.[18]

American troops remembered village dogs barking wildly and aggressively when their foot patrols entered a hamlet. The sight of the Americans frightened and agitated the dogs. Water buffaloes were also known to become distressed or angry in the presence of the Americans, who did not look, smell, or talk like any Vietnamese peasant. Corporal Kevin Macauley witnessed an odd event while in the jungle. “[I remember] watching a monkey jump out of a tree onto a patrol leader’s face and having him smack at it, trying to get it off himself in the middle of the night, and we’re all sitting there in total hostile territory laughing our heads off, watching this fool trying to protect himself from a monkey.”[19]

As the above accounts illustrate, the Vietcong, whether they knew it or not, had allies in the animal kingdom.


[1] Otto J. Lehrack, No Shining Armor: The Marines at War in Vietnam, An Oral History, (Lawrence: University Press of Kansas, 1992), 23.

[2] Philip Caputo, Rumor of War, (London: MacMillan London Limited, 1977), 60.

[3] S.L.A. Marshall, The Fields of Bamboo: Dong Tre, Trung Luong and Hoa Hoi, Three Battles Just Beyond the South China Sea, (New York: The Dial Press, 1971), 70.

[4] Tom A. Johnson, To The Limit: An Air Cav Pilot In Vietnam, (New York: New American Library Caliber, 2007), 29.

[5] S.L.A. Marshall, Battles in the Monsoon: Campaigning in the Central Highlands, Vietnam, Summer 1966, (Nashville, Tennessee: The Battery Press, Inc., 1967), 44.

[6] Lewis Sorley, ed. Vietnam Chronicles: The Abrams Tapes, 1968-1972, (Lubbock: Texas Tech University Press, 2004), 67, 274, 277.

[7] Sorley, Abrams Tapes, 670, 686; Arthur H. Westing, Ecological Consequences of the Second Indochina War, (Stockholm: Stockholm International Peace Research Institute, 1976), 56.

[8] Frederick Downs, The Killing Zone: My Life in the Vietnam War, (New York: W.W. Norton and Company, 2007), 48.

[9] Caputo, Rumor of War, 57.

[10] Lehrack, No Shining Armor, 150.

[11] Marshall, Battles in the Monsoon, 14.

[12] Harold G. Moore and Joseph L. Galloway, We Were Soldiers Once…  And Young, Ia Drang: The Battle That Changed the War in Vietnam, (New York: Random House, 1992), 27.

[13] Eric M. Bergerud, Red Thunder, Tropic Lightning: The World of a Combat Division in Vietnam, (New York: Penguin Books, 1994), 114.

[14] Lehrack, No Shining Armor, 148.

[15] Ron Steinman, The Soldiers’ Story: Vietnam in Their Own Words, 1999, Reprint, (New York: Barnes and Noble Books, 2002), 105.

[16] Peter T. White, “The Mekong: River of Terror and Hope,” National Geographic Magazine, Volume 134, Number 6, December, 1968, (Washington, D.C.: National Geographic Society, 1968), 737-787, p. 743.

[17] Steinman, The Soldiers’ Story, 103.

[18] John Laurence, The Cat From Hue: A Vietnam War Story, (New York: PublicAffairs, 2002), 812-813.

[19] Steinman, The Soldiers’ Story, 106.

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