High-altitude military parachuting (or military free fall (MFF)) is a method of delivering military personnel, military equipment, and other military supplies from a transport aircraft at a high altitude via free-fall parachute insertion. Two techniques are used: HALO (high altitude – low opening) and HAHO (high altitude – high opening).
In the HALO technique, the parachutist opens his parachute at a low altitude after free-falling for a period of time, while in the HAHO technique, the parachutist opens his parachute at a high altitude just a few seconds after jumping from the aircraft. Military HALO techniques date back to 1960, while in recent years, the HALO technique has been practiced by civilians as a form of skydiving.
In military operations, HALO is used for delivering equipment, supplies, or personnel, while HAHO is generally used only for personnel. In typical HALO/HAHO insertions the troops jump from altitudes between 15,000 feet (4,600 m) and 35,000 feet (11,000 m).
The origins of the HALO techniques date back to 1960 when the United States Air Force began conducting experiments that followed earlier work by Colonel John Stapp in the late 1940s through early 1950s on survivability for pilots ejecting at high altitude. Stapp, a research biophysicist and medical doctor, used himself in rocket sled tests to study the effects of very high g-forces. Stapp also solved many of the problems of high-altitude flight in his earliest work for the Air Force and subjected himself to exposure to altitudes of up to 45,000 feet (14,000 m). He later helped develop pressure suits and ejection seats, which have been used in jets ever since. As part of the experiments, on August 16, 1960, Colonel Joseph Kittinger performed the first high-altitude jump at 19.5 miles (31.4 km) above the Earth's surface. The first time the technique was used for combat was during the Vietnam War in Laos by members of MACV-SOG. SEAL Team Six of the United States Navy expanded the HALO technique to include delivery of boats and other large items.
The technique is used to airdrop supplies, equipment, or personnel at high altitudes when aircraft can fly above surface-to-air missile (SAM) engagement levels through enemy skies without posing a threat to the transport or load. In the event that anti-aircraft cannons are active near the drop zone, the HALO technique also minimizes the parachutist's exposure to flak.
For military cargo airdrops, the rigged load is cut free and rolls out of the plane as a result of aircraft deck angle (ADA). The load then proceeds to fall under canopy to a designated drop zone.
In a typical HALO exercise, the parachutist will jump from the aircraft, free-fall for a period of time at terminal velocity, and open their parachute at a low altitude. The combination of high downward speed, minimal forward airspeed, and the use of only small amounts of metal helps to defeat radar and reduces the amount of time a parachute might be visible to ground observers, enabling a stealthy insertion.
The HAHO technique is used to airdrop personnel at high altitudes when aircraft are unable to fly above enemy skies without posing a threat to the jumpers. In addition, HAHO parachute jumps are employed in the covert insertion of military personnel (generally special operations forces) into enemy territory, in circumstances where the covert nature of an operation may be compromised by the loud noise of parachutes opening at low altitude.
HAHO jumps also allow a longer travel distance due to increased under canopy time, allowing travelling distances of more than 40 miles (64 km).
In a typical HAHO exercise, the jumper will jump from the aircraft and deploy the parachute at a high altitude, 10–15 seconds after the jump (typically at 27,000 feet (8,200 m) or so). The jumper will use a compass or GPS device for guidance while flying for 30 or more miles (48+ kilometres). The jumper must use way points and terrain features to navigate to their desired landing zone, and correct their course to account for changes in wind speed and direction. If deploying as a team, the team will form up in a stack while airborne with their parachutes. Usually, the jumper in the lowest position will set the travel course and act as a guide for the other team members.
Whilst in the British Special Forces (22 SAS), due to his extensive skydiving background, Charles "Nish" Bruce was pivotal in the original trials and development of the HAHO tactic now routinely used as a conflict insert for Special Forces.
All types of parachuting techniques are dangerous, but HALO/HAHO carry special risks. At high altitudes (greater than 22,000 feet [6,700 m]), the partial pressure of oxygen in the Earth's atmosphere is low. Oxygen is required for human respiration and lack of pressure can lead to hypoxia. Also, rapid ascent in the jump aircraft without all nitrogen flushed from the bloodstream can lead to decompression sickness (also known as caisson disease or "the bends").
A typical HALO exercise will require a pre-breathing period (30–45 minutes) prior to jump where the jumper breathes 100% oxygen in order to flush nitrogen from their bloodstream. Also, a HALO jumper will employ an oxygen bottle during the jump. Danger can come from medical conditions affecting the jumper. For example, cigarette smoking, alcohol and drug use (including histamine antagonists, sedatives, and analgesics), anemia, carbon monoxide, fatigue and anxiety can all lead to a jumper being more susceptible to hypoxia. In addition, problems with the oxygen bottle and during the changeover from the pre-breather to the oxygen bottle can result in the return of nitrogen to the jumper's bloodstream and, therefore, an increased likelihood of decompression sickness. Theoretically, a single breath of atmospheric air may elevate the jumper's arterial nitrogen level to dangerous levels. A jumper suffering from hypoxia may lose consciousness and therefore be unable to open his parachute. A jumper suffering from decompression sickness may die or become permanently disabled from nitrogen bubbles in the bloodstream, which causes inflammation of joints.
Another risk is from the low ambient temperatures prevalent at higher altitudes. At an altitude of 35,000 feet, the jumper faces temperatures of –45 °C (–50 °F), and can experience frostbite. However, HALO jumpers generally wear polypropylene knit undergarments and other warm clothing to prevent this.
HALO carries the additional risk that if the parachute fails to deploy or lines become tangled, there is less time to resort to the reserve (back-up parachute) or untangle the lines, though the reserve is the best option if this were to occur.Free fall parachute insertions were utilized during Operation Iraqi Freedom, as a means of bypassing enemy early warning systems.