A declassified United States Army regulation from January 1968, buried for decades in medical archives, reveals a stunning operational directive for troops fighting in Vietnam: leave your underwear behind. The one-page memorandum, signed on behalf of the commanding general of US Army Vietnam, was not a joke. It was a desperate response to a silent enemy that was destroying combat effectiveness faster than enemy fire—skin disease.
The directive, USARV Regulation 40-29, dated January 10, 1968, titled “Prevention of Skin Disease Among Troops Operating in Inundated Areas,” explicitly states that underclothing “reduce ventilation of the skin.” It urged commanders to discourage—not ban—underwear during field operations. The reason: in Vietnam’s relentless heat and humidity, wet cloth trapped against the skin became a breeding ground for fungal and bacterial infections.
But the men who first understood this grim arithmetic were not waiting for orders. The Long Range Reconnaissance Patrols, or LRRPs—four- to six-man teams inserted deep into enemy-controlled territory—had already stripped down to survive. They knew that a single rash could cost a team its stealth, its mobility, or a man’s life.
These teams operated with no backup within an hour’s flight, no resupply, no shelter. Whatever they wore when the helicopter dropped them off was what they wore for days on end. In the jungle, skin stays wet.
Wet skin softens, tears, and becomes infected. One Army dermatologist recorded that a combat unit could lose 70 to 75 percent of its personnel to inflammatory skin disease of the feet alone if feet were continuously wet for more than 72 hours.
The toll was staggering. Peer-reviewed dermatology research published in the Journal of the American Academy of Dermatology confirms that skin conditions were the single most common reason American soldiers sought medical care in Vietnam, accounting for 7. 4 percent of all admissions and 12.
2 percent of outpatient visits. The Army Medical Department’s own official history puts the cost in man-days lost: roughly 66,400 in 1967, 64,800 in 1968, 50,800 in 1969, and over 80,000 in 1970.
Malaria was worse, costing between 167,000 and 228,000 man-days in those same years. But skin disease was the silent saboteur no one expected. It hit hardest in the units that could least afford it—the recon teams that depended on every man being fully functional.
In the Mekong Delta, the 9th Infantry Division surgeon reported in 1968 that after five days in the paddies, one battalion’s strength had been cut by as much as a third—not by the enemy, but by immersion foot.
A memorandum from the 9th Division in October 1968 warned commanders that foot and boot area disease could affect 35 to 50 percent of a unit’s combat strength after 72 hours in the water. Operations were capped at 48 hours followed by a full day dry. One Army dermatologist recorded that before those measures came in, a unit could lose 70 to 75 percent of its personnel to inflammatory skin disease of the feet alone after 72 hours of continuous wetness.
The LRRPs had already figured it out. John Stryker Meyer, a MACV-SOG recon veteran, wrote that to avoid rashes, infections, and fungus, he and his teammates did not wear underwear or socks. No SOG recon man wore a helmet, helmet liner, or body armor.
They went without soap, deodorant, toothpaste, and aftershave. Scent discipline was as critical as noise discipline. Some teams even ate the same food as the North Vietnamese to mask their odor.
But the internet has inflated this into myth. You will find claims that Vietnamese trackers could smell American aftershave from two kilometers away, that deodorant gave away a team at 500 to 800 meters, that scent discipline reduced enemy contact by 43 percent. None of those figures trace to a primary source—no captured document, no after-action report, no memoir.
The trail runs back to auto-generated content with no citations. The best-documented scent detection runs in the opposite direction: American veterans repeatedly describe how they could smell enemy positions from nuoc mam and local tobacco.
The regulation itself was a medical recommendation, not an order. It did not ban underwear; it “discouraged” it. Commanders were left to apply it where necessary.
The same directive told troops to wear boots and socks only when necessary, to swap into shower thongs in base camp, and to stop starching field clothing because starch cut ventilation. It is reproduced in full in the US Army’s own dermatology textbook, published by the Borden Institute.
The Army was redesigning everything. The tropical combat uniform, introduced in 1963 and reaching line infantry by 1966, was lighter, had slanted bellows pockets, and a loose cut to allow airflow. But the hardest problem was feet.
The jungle boot was designed to drain, not keep feet dry: canvas and leather upper, brass eyelets low on the instep, ventilating insole, and a steel plate after punji stake injuries. In 1968, the Panama sole became standard.
None of it was enough. The Army’s own medical history, “Skin Diseases in Vietnam,” states that superficial fungal infections were the most common and most troublesome dermatologic condition. Hardly anyone escaped some form of fungal skin infection during his tour.
After long patrols in swamp and flooded paddy, as many as half the men in a unit developed immersion injuries, with the worst cases evacuated to rear hospitals.
The treatment was absurdly simple: clean the skin, dry it, get weight off, get sunlight, get out of the water. One American brigade bought 5,000 pairs of rubber shower thongs and capped continuous wet exposure at 72 hours. It cut its rate of tropical immersion foot to 10 percent or less.
A brigade solved a combat effectiveness problem with flip-flops.
The answer to the question that has haunted Vietnam War history for half a century is not a myth about a secret ban. It is a one-page memo born from arithmetic in a Saigon medical office. The jungle was costing the United States Army tens of thousands of working days a year.
The men walking into the tree line were not thinking about regulations. They were calculating what would 𝓀𝒾𝓁𝓁 them slower. They left behind underwear, socks, soap, toothpaste.
Then they went out for four more days, counting on nothing but silence and the hope that their own bodies would not betray them.
The full text of USARV Regulation 40-29 is available in the Borden Institute’s dermatology textbook, and links to all primary documents have been made public. This is the version that is actually in the archive, not the version that gets repeated until it sounds true. For the men who were there, the sacrifice of comfort—and of modesty—was a price they paid to stay alive.
