A recent special operations exercise in California in early July revealed one of the dangers of military free-fall operations.

During the exercise, a British commando’s primary parachute failed to deploy properly. The operator deployed his reserve parachute, but it didn’t have enough time to inflate properly, leaving him to fall 15,000 feet.

The malfunction meant he fell straight through the roof of a civilian house, landing in the kitchen. Surprisingly, the British commando wasn’t seriously hurt, only suffering minor injuries, according to local law enforcement.

For personal security purposes, the British Ministry of Defense didn’t release the name or the unit of the lucky parachutist.

However, only a select few British special operations units receive military free-fall training. So it’s safe to assume that the commando is a member of the Special Air Service (SAS), Special Boat Service (SBS), the Special Reconnaissance Regiment (SRR), the Special Forces Support Group (SFSG), or the Pathfinders.

Many more U.S. military units receive free-fall training, including the Army’s Delta Force and Ranger Reconnaissance Company and the Naval Special Warfare Development Group (formerly known as SEAL Team Six), as well as select Army Green Beret teams and Air Commandos.

Free-fall is a great insertion method for special operations units. When done by well-trained commandos, and when everything goes right, it’s stealthy and accurate.

Not All Parachuting Is the Same

Static-line and free-fall are the military’s two parachuting methods.

Static-line parachute training is a staple of every special operations pipeline in the U.S. military, with a lot of support troops going through it too. Free-fall training is generally reserved for select individuals or teams.

However, some units, such as the Navy SEAL teams and Army Green Berets, have incorporated free-fall into their pipelines in order to be more competitive and relevant in future contingencies.

The more common static-line method is what you imagine when you hear about paratroopers. It’s what the 82nd Airborne Division uses and has historically been the preferred method for large-scale drops. This is how American and British paratroopers jumped into France on D-Day in 1944 and how the Rangers jumped in Grenada in 1983.

During static-line jumps, the parachute’s ripcord is connected to the aircraft. Once a paratrooper exits the aircraft, the cord is pulled, and the parachute deploys. If there’s a malfunction or the parachute gets tangled, the paratrooper has a reserve chute.

Static-line jumps occur in low altitudes, between 500 and 1,500 feet, giving paratroopers little time to fix malfunctions.

There have been jumps from ever lower altitudes.

The Rhodesian Light Infantry, a now deactivated special operations unit similar to the U.S. Army’s 75th Ranger Regiment, used to jump at around 200 feet — so low that the troopers didn’t pack a reserve parachute as there would be no time to deploy it. (A soldier from the unit also holds the world record for the most static-line combat jumps with an astounding 73.)

Static-line is certainly the easier method as it requires almost no skill. The hardest part is the landing, which, if not done properly, can cause broken ankles, dislocated knees, or worse.

Free-fall: Masters of the Air

Free-fall parachuting is the military equivalent of skydiving but with a major twist. It requires hundreds of hours of training in the classroom, on the ground, and in the air.

Whereas skydiving requires little skill and only a parachute, in free fall a commando carries tens if not hundreds of pounds of gear, a burden that can be lethal on an untrained person. Commandos also often jump at night and in adverse weather conditions.

“[Military free-fall] ops are hard to master. It takes a lot of training to be able to fly [just] you and your equipment effectively and safely,” John Black, a retired Special Forces warrant officer, told Insider.

“Now you add a team of individuals, and it becomes much more difficult. A lot of training goes into getting a team efficient to not only jump together but also to land safely in the same spot,” added Black, who was qualified for free-fall jumps.

Army Special Forces spent “tons of hours in the wind tunnel, dozens of jumps, and endless rehearsals go into any training. The smallest mistake can cause a much larger issue,” Black said.

There are two free-fall categories — High Altitude High Opening (HAHO) and High Altitude Low Opening (HALO) — each tailored to different operational needs.

During a HAHO jump, a special operator would deploy his parachute soon after exiting the aircraft at somewhere between 30,000 to 25,000 feet and then glide to the target. Training and specialized equipment would allow him to traverse anywhere from 20 to 40 miles while in the air, making HAHO great for clandestine insertions, even across borders, as the aircraft can stay away from the target area and thus not alert the opposition.

Things are a little different during a HALO jump. A commando would exit the aircraft, free fall, and then deploy his parachute close to the ground. Although HALO jumps don’t allow for traveling great distances, they are ideal for large team insertions as it’s easier for the operators to group up in the air and then land close together.

Delta Force, DEVGRU, and the Ranger Reconnaissance Company are known within the U.S. special operations community for their superb free-fall capabilities. Some of their operators have thousands of jumps.

The majority of special operators attend the U.S. Army’s John F. Kennedy Special Warfare Center’s Military Free Fall School in Yuma, Arizona, for free-fall training.

But as the recent incident with the British commando showed, free-fall operations are packed with danger. There have been about 20 U.S. military deaths during static-line and free-fall training jumps over the last 15 years.

“Jumping out of a perfectly good aircraft is inherently a dangerous operation. It sometimes becomes more dangerous when newer jumpers are added that are less familiar with the equipment and other jumpers,” Black said.

This article was written by Stavros Atlamazoglou and originally published on the Insider.