The Cavalry Stetson is a Cavalry tradition within the United States Army.
Cavalry Stetson Wikipedia
The Cavalry stetson was the headgear typical of cavalrymen during the late 18th century into the 19th century, including the Indian Wars and the Civil War. Before John B. Stetson, for whom the hat is named, introduced the Boss of the Plains hat in 1865, troopers wore hats in a similar style, but quickly adopted the Boss of the Plains as an unofficial standard.
In the modern United States Army, the Stetson was revived as an unauthorized, unofficial headgear for the sake of esprit de corps in the Air Cavalry. Because they are not authorized by AR 670-1, the regulation for wear and appearance of the uniform, wear and use of the Stetson and the similar spurs is regulated by the unit commander.
On April Fools' Day, 2011, the U.S. Army released a humorous statement that the official black beret of the Army would be replaced by stetsons. Below is an excerpt from the full announcement:
WASHINGTON, APRIL 1, 2011 -- In a fingertip-to-the-brim nod to its American frontier history, the Army is changing hats again - returning to the tumultuous days of the horse Cavalry in the wild west and adopting a dark blue Stetson as the official headgear for the current force of 1.1 million Soldiers. "We figure the Stetson will be popular with the troops," said Sgt. Maj. Bob S. Stone, Army Uniform Board headgear task force president. "It's been a while since we have changed the headgear, so it's time. Plus a Stetson is functional and down right American." But reminiscent of the controversial switch from the garrison cap to the black beret, the Army faces opposition from one community deeply opposed to losing its special identity with the Stetson - the Armor branch. "Why in the heck are they doing to us what they did to the snake-eaters'" asked one officer familiar with the board's deliberations. "If you ain't Cav, you ain't ought to be wearing a Cav hat. That just ain't right." [...] The Army's official adoption date of the Stetson will be April Fool's Day, 2012.
The statement was supplemented by pictures of soldiers with Cavalry Hats photoshopped over their berets, including a military working dog toting a stetson.