For those of you who earned your 'scuba bubble' in the military or who have an interest in civilian scuba diving.

Rebreather (RB) technology both in the military and civilian sectors has come a long way in the last 8 years.  They are still pricy, require extensive training, and attention to detail, but some systems out there are amazing options as underwater life support systems.  The obvious application in the military is undetected infiltration.  On the civilian side you can observe marine life closer since it is not scared off as easy as when using open circuit UBAs.  For both civilian and miliatry use rebreathers have a number of advantages and disadvantages.

Apart from 'silent diving' other advantages: more efficient use of your gas supply thus increasing your bottom time, optimized decompression parameters, and with some high speed mixed gas systems increased depth while avoiding oxygen toxicity or huge inert gas intake.  For more on the advantages and disadvantages visit the 'bishopmuseum' link below.

Here is how rebreathers work and how they differ from 'open circuit scuba' systems:

http://www.bishopmuseum.org/research/treks/palautz97/rb.html#FurtherReading

Civilian rebreather technology:

http://www.metacut.com/rebreathers/reb_pages.htm

http://www.halcyon.net/rebreather/rb80_features.shtml

http://www.steammachines.com/

http://www.ambientpressurediving.com/

http://www.rebreather-azimuth.com/rebreather-engl.html

http://www.silentdiving.com/index.php

Training:

http://www.nauitec.com

Types of rebreathers -->  OR: Oxygen Rebreather, SCR: Semi-closed Circuit Rebreather, and CCR: Closed Circuit Rebreather.

Beware that even if you are a certified scuba diver these systems require extensive additional training and experience.  Some systems can go from anywhere between $3,000 and $10,000 (depending on the model) and the certification class for most of them will put you behind at least $500.  Certification and training is specific to the system that you will be diving.  Rebreathers require much more attention to detail and pre-dive prep/checks than open-circuit systems.  You simply can't be lazy or oversighted with rebreathers, same as packing a chute for freefall jump.

If you are a scuba instructor you must have over 100 hours diving a specific rebreather model before you can teach it.

I've dove both ORs and SCRs before but I've never owned one.  When I return stateside I would like to buy the Halcyon RB80.

RLTW!

"The degenerative and loony should never be denigrated but, rather, thanked. In their absence, the rest of you would be obliged to fill congressional seats... positions naturally unsavory to the sane and honorable."

Thorax

Steve, yes I plan to teach on the side again on the island.  I recently wrote to U.S. Customs and Border Protection in Detroit requesting a transfer back to PR.

As for rebreathers you are right.  With "OR" systems you do have to maintain your depth around 25 feet due the possibility of oxygen toxicity beyond 30 feet.  Military Spec Ops (LAR-V) rebreather divers (Army, Air Force, Marines, and Navy) are very aware of this.  However, they are not diving to go deep, they are using the system for undetected underwater infiltration around 25 feet.  You don't see much use of ORs in the civilian sector, scientific divers do use them for research above 30 feet.  The PRIZM-TOPAZ that Ertman mentions (a CCR) with the proper training and 'diluent' in the system can be dove to an amazing 300 feet.  The Topaz is a constant PO2-mixed gas CCR.  I believe the same holds for systems like the CIS-LUNAR.

As for current civilian SCRs and CCRs that is the beauty of them.  Pretty much all of the more high speed systems allow you to dive well beyond 30 feet (that is the whole idea), some even deeper than the scuba recreational limit of 130 (for example the Topaz).  They do this by regulating the PO2 in your breathing mixture so it remains well below 1.6 the entire dive (between 1.3 and 1.5), thus avoiding oxygen toxicity regardless of depth and at the same time keeping a lot of inert gas out of your blood and tissues thus giving you optimized decompression parameters for your ascent.  Check out the "how rebreathers work" link above.

Nitrox SCR systems like those from DRAGER (Dolphin and Ray) are designed for the 'recreational' rebreather diver who has no desire to descend beyond 130 feet.

Ertman, I've read a lot about the CIS-LUNAR, a bad ass system.  Some record breaking cave dives were accomplished with that system.  I also think that the PRIZM is a sweet CCR.  How long you've been diving?  AATW! 

Are rebreathers eventually going to replace "normal" scuba gear? Also, how much more "underwater" time do the re-breathers give you?

Just a curious scuba noob...