Quick: you're a Union commander in the US Civil War. You've got a major conflict to fight in varied terrain and climate conditions. You're going to want to protect your soldiers from the elements. You're in North America in the mid-19th Century, and there aren't exactly a lot of buildings you can commandeer – not for armies that number in the tens of thousands. You need a temporary shelter that can be set up quickly and won't fall down or catch fire.

How about a Sibley tent? Too bad its inventor went over to the enemy.

Major Sibley's Tent

Major Sibley of the US Army was a West Point graduate, which means he had studied engineering. He'd fought in the Second Seminole War and in the Mexican-American War. He'd been on frontier duty in Texas. He probably got the idea for his tent from the tipis of the Plains Native Americans.

The great advantage of a Sibley tent is the fact that it rests on a single pole, 12 feet (3.6m). The pole is held up by a tripod, which the soldiers also used to hang pots from over a cooking fire. The tent canvas, 18 feet (5.5m) in diameter, is secured by 24 tent pegs. It can hold a dozen men easily, and the hole in the top allows for indoor cooking with a stove (which Sibley also invented), or just a firepit in the centre of the tent.

There was a bit of a problem with that cooking business in practice, as a soldier remembered.

At the top is a circular opening, perhaps a foot in diameter, which serves the double purpose of ventilation and of passing a stove-pipe through in cool weather. This stove-pipe connected with a cone-shaped stove suited to this shape of tent, which stood beneath the tripod. A small piece of canvas, called a cap to which were attached two long guys, covered the opening at the top in stormy weather. It was not an unusual sight in the service to see the top of one of these tents in a blaze caused by some one having drawn the cap too near an over-heated stove-pipe…
– JD Billings, Hardtack and Coffee, p 47

The Sibley tent had the advantage of being easy to assemble and efficient to maintain (if you didn't set the top flap on fire). But it had its drawbacks in terms of comfort, as the same soldier points out.

These tents are comfortably capacious for a dozen men. In cold or rainy weather, when every opening is closed, they are most unwholesome tenements, and to enter one of them of a rainy morning from the outer air, and encounter the night's accumulation of nauseating exhalations from the bodies of twelve men (differing widely in their habits of personal cleanliness) was an experience which no old soldier has ever been known to recall with any great enthusiasm.
– JD Billings, Hardtack and Coffee, p 47

The Sibley tent went out of general use in 1862, largely because they were so bulky and hard to transport. The army continued to use them for winter quarters and training camps. After the Civil War, state militias still used them.

Further Adventures of Sibley and His Tent

Sibley patented his tent in 1856¹. It was a successful design. The US Department of War agreed to pay him $5 for every tent they produced. Since the Union Army used 44,000 Sibley tents during the Civil War, that would have been a nice chunk of change. But Sibley, who was from Louisiana, decided to join the Confederate Army. The Confederates made him a general, but the Union army refused to pay him his tent royalties, even after the war. Sibley went on to serve as a general in the Egyptian army.

The Sibley tent continued to be popular with the US military, and variations on it and other bell tent designs were used by soldiers and explorers throughout the 19th Century. Nowadays, the design is popular with the 'glamping²' crowd.