Mules don’t exist in nature. They are an artificial product of human ingenuity, and like many such products, it didn’t take long before they found a place in the grim business of war.

A mule is the offspring of a male donkey and a female horse. The genetic mismatch of these species causes sterility, but the hybrid creates a pack animal that combines a horse’s strength and intelligence with a donkey’s sure-footedness and endurance. In addition, a mule’s hide and hooves are tougher than a horse’s, and endure heat better. They carry heavier loads for longer distances, and eat a third less than horses doing the same work. On the downside, mules are temperamental: The phrases “stubborn as a mule” and “kicks like a mule” reflect the experiences of generations of “mule skinners.”

Mules were first bred as early as the 4th millennium B.C., in Anatolia, or possibly Central Asia, where wild horses and wild donkeys lived near settled humans. Sumerian clay tablets from about 3000 B.C. price mules at 20 to 30 shekels of silver (220 to 330 grams, or 7 to 10.5 troy ounces): seven times the cost of donkeys. The Hebrew Bible has 17 references to mules, and the ancient Greek Olympics featured mule cart races. In 107 B.C. the Roman general Marius (uncle of Julius Caesar) streamlined the legions, drastically reducing the number of pack animals and baggage carts. Legionaries nicknamed their heavy backpacks “Marius’ mules.”

Like so many American stories, American mule breeding starts with George Washington.

He wanted to breed stronger mules for plantation work, but Spain banned the export of its excellent Andalusia donkeys. In 1785, King Carlos III sent Washington a diplomatic gift: two females and a male. The following year, the Marquis de Lafayette added some fine Maltese donkeys to Mount Vernon’s breeding stock. By 1808, these animals and their kin had an estimated 855,000 descendants working on farms, mostly in the South.

During the Civil War, the Union Army used about one million mules to pull supply wagons. In 1864 alone, Army quartermasters purchased 87,791 mules. However, with their sensitive ears and strong sense of self-preservation, mules tended to panic at the sound of the guns. Although Kentucky, Missouri, and Tennessee bred the best animals, the Confederacy used half as many, often requisitioned from farmers. Mule drivers were often slaves; when they escaped to Union lines, they brought hard-earned skills and experience in handling and caring for the ornery beasts. Contemporaries joked that Lincoln worried more about the comfort of Army mules than of his officers. Jefferson Davis had no such qualms, and at the siege of Vicksburg in 1863, the starving garrison was reduced to eating their mules.

“The mule was ridiculed for being the son of a donkey; he replied, “The horse is my uncle.”

– Arab proverb

In 1869, Sir Garnet Wolseley (1833-1913), the British officer mocked by Gilbert & Sullivan as “the very model of a modern major-general,” published The Soldier’s Pocket-book for Field Service, compiling decades of practical war experience. Here are Wolseley’s logistics planning figures for a global empire:

	Animal Speed (Miles per Hour)	Pack Load (Pounds)	Draught Load (Pounds)	Work Day (Distance in Miles)
Camel	2.5	300-600	1,000	20
Elephant	3.5	800-1,200	8,000	15-20
Horse	4.0	250-400	350	15-16
Human	2.5	40-80	120-150	4-8
Mule	4.0	150-300	500	15-16
Ox	2.2	160-200	300-500	4-6
Reindeer	18~90	300	300	50-100 by sleigh

“Draught load” presumably includes the weight of a cart or sled, plus its payload.

Many 19th century armies organized mountain units, equipped with “pack howitzers” – light cannon (typically 65 mm to 75 mm) that broke down into several mule loads for travel over roadless rough terrain.

The famous Marine Corps Small Wars Manual (1940) noted that:

“The mule is the ideal pack animal for supply trains, pack trains with foot patrols, and pack trains with detachments mounted on mules. The mule has certain advantages over the horse, which fit him for this work, namely:

1. The mule withstands hot weather better, and is less susceptible to colic and founder than the horse. [“Colic” describes various digestive disorders that can be fatal to horses; “founder” is a crippling inflammation of the hooves typically caused by overeating].
2. A mule takes better care of himself, in the hands of an incompetent driver, than the horse.
3. The foot of the mule is less subject to disorders.
4. The mule is invariably a good walker.
5. Age and infirmity count less against a mule than a horse.”

“The average Marine can be trained in a fairly short time to pack mules more securely and more rapidly than the average native mule driver, and in regions where pack transportation is used, every Marine should be taught to pack. The use of Marines as packers … has many advantages … it may be undesirable or impracticable to include native packers in a combat patrol. The hiring of native packers always gives the populace warning that the column is about to move out.”

In 1915, Gunnery Sgt. Daniel Daly (1873-1937), one of only 19 men awarded the Medal of Honor twice, led a mounted patrol of 38 Marines against a large force of Haitian insurgents. Ambushed crossing a stream, they lost 12 horses and the pack mule carrying their only machine gun. In darkness, under fire, Daly dove repeatedly to locate the dead mule, recovering the weapon and ammunition, which weighed almost twice as much as he did, and carried the load through the jungle to rejoin his men. By daylight he had assembled and emplaced the gun. At dawn the Marines attacked, scattering the enemy.

One lesson of World War II was that mules are not good fliers. In 1944, an Indian division was airlifted with its pack mules into the remote town of Imphal, under Japanese attack. The rough flight on board C-47s upset the animals so much they lost bowel and bladder control. Urine leaking through the cabin floors caused electrical shorts, and a few fires – luckily, none fatal. Liberty ships proved much more mule-friendly: as many as 320 could be carried across the Atlantic in one shipload.

In 1957, the U.S. Army sold off its last 136 mules as an anachronism, unsuitable for the nuclear age. But in the 1980s, when Afghan Mujahedeen took on the occupying Soviet Army, there was an urgent need for pack animals. When Egypt got a CIA contract to provide 2,500 mules at $1,300 each, Pakistan raised objections about equine disease risks, and the Egyptians provided each animal with an ID card and a vaccination certificate! The Pakistanis became so cranky they wouldn’t let CIA transports leave mule manure in-country, and made cargo planes carry it back to Europe. A decade later, mules were a key component in the U.S.-led effort in Afghanistan, where they were used by the famous Special Forces “Horse Soldiers,” in Fall 2001. Mules continue to be a critical logistics/transport resource today.

Today, the Marine Corps Mountain Training Center (MWTC) in the Sierra Nevada, 21 miles (33.8 kilometers) north of Bridgeport, Calif., is responsible for all U.S. military pack animal training. The two-week course covers the care, feeding, loading, packing, and safe handling of animals on narrow mountain trails. Today’s city and suburban-bred troops are usually apprehensive and unfamiliar with animals other than dogs and cats. One useful tip: Be alert when the ears flare out – mules can often sense an ambush before troops can. A Mountain Medicine course teaches use of mules for casualty evacuation (along with first aid for injured beasts). The center maintains a stable of up to a few dozen donkeys, horses and mules to support training.

In military history, thoroughbred stallions may get the statues and the glory, but we should remember that humble mules did much of the heavy hauling.