H.A.L.O.High Altitude/Low opening (HALO) jumping from upwards of 36,000 feet on oxygen. At that altitude the tempurature is subzero, and it is common for your goggles to freeze and shatter, and your eyeballs to freeze shut. This type of jumping is very dangerous because of the effects of hypoxia - lack of oxygen. Hypoxia can cause a man to lose consiousness in an instance with no prior warning. One second you are checking your altimiter, the next you are out. bam - no warning. If this happens while in freefall it can lead to sudden deceleration trauma - you guessed it - death upon impact. Equipment common to all freefall ops are the Ram AIr, altimeter, FF2 (automatic pressure activated rip cord pulling device - it is supposed to pop your chute if you don't when you descend past a pre-set altitude). Hook knife, helmet and goggles, gloves, oxygen bottle and mask (if jumping over 12,000 feet) and a sturdy pair of jump boots are a must for ankle support.
H.A.H.O.High Altitude/High Opening jumping is an extremely difficult form of insertion which requires a tremendous amount of training as an individual and team. A typical HAHO profile has a squad jumping out of either a commercial aircraft or military craft with a commercial IFF signature in the normal air traffic lanes so as to not raise suspicion. The jumpers will exit the aircraft at a high altitude - say 30,000 feet, and deploy their parachutes in ten to fifteen seconds at an altitude of 27,000 feet or so. The squad will form up in a stack in the air, with the low jumper setting the course and acting as the guide. The squad will fly upwards of thirty or more miles in formation, using a compass, way points and terrain features to navigate to their targeted landing zone. Along the way, the navigator must correct his course for changes in winds speed and direction, making for a tricky navigation problem. The only thing more difficult than navigating while flying a Ram-Air is navigating with an attack board underwater. Nonetheless, HAHO free fall operations can get SEALs where they want to be clandestinely and ready to wreak havoc!
Abstract from
http://www.navyseals.com/equip/air.html
