Editor’s note: The following piece on the Dreager LarV was written by retired Delta Force Master Sergeant George E Hand IV. While this piece discusses special operations equipment, it does not reveal any classified information.
Recreational SCUBA diving with standard compressed air can give a diver about an hour of bottom time. That of course is largely dependent on the depth the diver spends his time at; the deeper one goes the less time he has at depth. A rule of thumb is 60 feet for 60 minutes and then you should come out of the water. The longer you stay at depth also governs how long you must wait on dry land before you can go back to SCUBA diving.
Imagine now being able to stay underwater for more than four hours without ever even exhaling a single bubble. The military has a system that “breathes” pure oxygen (O2) and is based on a closed gas system. SCUBA features an open gas system; that is where each exhaled breath is released out into the water and rises to the surface where it stirs up the water and creates an unmistakable profile that there is a person diving down below.
Draeger LarV: The Third Lung of Combat Divers
Related: NAVY SEAL DIVES WITH SHARKS
The soldier above is decked out in a slight variant of the LarV. The blue bottle at the bottom of the Draeger case is the pure oxygen supply bottle. Inside the LarV case is the third lung and the canister that “scrubs” CO2 out of an exhaled breath, and the regulator that allows fresh O2 to enter the breathing cycle.
The LarV’s third lung bag is filled with O2 at the beginning of the dive. There are two breathing hoses on the rig; one is for inhalation and the other is for exhalation.
1. A breath of O2 is drawn from the breathing bag through the breathing hose
2. The breath is exhaled into the exhalation hose that leads to the scrubber canister where the CO2 is scrubbed from breath; the scrubber is a caustic soda-lime solution that has a great affinity to absorb C02 from a gas; it looks for all the world like cat litter (see image below of soda-lime product in a canister).
3. the exhaled breath leaves the scrubber canister and returns to the breathing bag with the residual O2 where it is re-breathed by the diver.
4. As the O2 is in your breath, that is, the volume of breathable gas in the third lung bag becomes depleted, the regulator detects the drop in pressure and refills the third lung. There is also a large override button on the top front of the LarV case that allows the swimmer to refill the bag at will. Sometimes the diver just doesn’t agree with how much O2 the LarV thinks he needs and feels the urge to override the regulator
All told, a diver can stay under the surface of the water for three to five hours depending on many variables; a few of which are:
1. Water temperature; soda-lima scrubs better in cooler water temperature. After a dive the soda-lime can is very warm to the touch; it is part of the chemical reaction of the scrubbing process that produces the heat.
2. Individual’s level of physical conditioning allows him to burn more or less of his oxygen supply.
Some nice and important features of closed (UBA) vs open-circuit (SCUBA) systems is that they’re lighter weight, less cumbersome, very quiet, and emit no bubbles!
Undersea life behaves quite a bit differently to a diver who is emitting no bubbles; you just seem more to them like you belong underwater than a SCUBA diver who is off-gassing tremendous bubbles. Those tell-tale bubbles also, of course, reveal to persons on the surface that there are divers below. That one feature makes SCUBA unsuitable for military tactical work.
One of the disadvantages of the military’s tactical UBA breathing apparatus is that it is dangerous to dive deep, having a maximum safe depth of 33 feet of seawater. If you dive much farther below that depth, oxygen become poisonous to the Central Nervous System (CNS). O2 poisoning can cause violent convulsions — it is not ideal for a diver to be rolling around and choking on his tongue at his max depth.
If a diver becomes head-down vertical while diving the LarV, fluid from the chemical reaction in the scrubber can leak down through the inhalation hose and give the diver the most disturbing taste — it’s what is known in the community as a “caustic cocktail.” As you might have guessed, that the fluid is very harmful to the diver.
The Draeger LarV rebreather, in its several configurations, remains one of the best tactical clandestine advantages weapons in the Army Special Forces as well as in the SEAL community today. Imagine having one of these systems on your next recreational dive operation hunting for lobster and other undersea treats that are no longer darting away in fear of your presence. Oh, the possibilities!
By Almighty God and with honor