> Rich, the military never had the Mark 15.5 only the Mark 15, predessor to 
> the 15.5, and the Mark 16 which is the same as the 15.5 but with 
> different primary and secondary guages. 

Then why, among my stack of NEDU reports, do I find various evaluations 
of the "Mk 15 1/2 Closed Circuit UBA"? (e.g., Rept. No. 10-84)

> The EX-19 project was (note past tense 
> because the project was scrapped because the 16 is good enough) 
> to 
> produce a rebreather that was an order of magnitude higher tech than the 
> Mark 16. The EX-19 concept had nothing to do with whether the Mark 16 or 
> any predessors were not wonderful devices. 

Hmmm....I'm not sure what would constitute "good enough" the way the 
military budget has been slashed in recent years...but I sincerely wish 
that the EX-19 program had been allowed to continue, because with their 
resources (both $$$ and people), I'm sure a lot of important advances in 
rebreather technology would have come out of it.

> I would be willing to bet, if 
> the truth were known, that Bill Stone had Mark 15.5's for his early work 
> and the Cis-Lunar evolved from that rebreather. You might even say that 
> the Mark 15.5 is the foundation upon which the Cis-Lunar was designed. 

I don't know the history well enough, but I do know there are some
fundamental differences in design concepts between the two units (you
know, trivial things like counterlung placement, electronic and manual
control principles, scrubber canister design, etc). What you suggest above
might be akin to saying that the Mark 15.5 grew out of the foundation laid
by the Fleuss Mask. My understanding is that the reason Stone started at 
ground zero on rebreather design was that he wasn't happy with the 15.5 
for cave diving.  He could have saved a hell of a lot of money by just 
modifying the 15.5 to meet his needs.  Unless he's stupid (and I happen 
to know that he's not), he must have had some reason for re-inventing the 
wheel.

On the other hand, what makes the 15.5 so attractive is the incredible 
amount of testing that it has been subjected to.  Over the past year, 
I've learned a lot about how important it is to have real-world test time 
on units in a variety of conditions, and the 15.5 is near the top of the 
heap as far testing goes for mixed-gas fully closed 'breathers.

> You know, biologists have known for a long time that if earthlings 
> worshipped anything it ought to be the sun for providing the oxygen we 
> breathe and the food we eat. In the same vein, rebreather fanciers ought 
> to worship the MK 15.5 as the fountain of all rebreatherness and as such 
> they ought to bow their heads when we MK15.5 owners pass by with our 
> units. Rod 

Huh?  The sun provides the oxygen? wha...?  Did I miss something? I 
always though that the sun provided electromagnetic energy.

But on the rest of the stuff (e.g. head bowing, etc.), I fully agree.

Aloha,
Rich

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