E.J.
1852
An in deep view about the Benrus Type I Sterile.
In the early ´70s some awesome watches born. Them are higly prized by collectors and endlessly copied/hommaged by other firms ... The Desirables Benrus Type I & II.
These amazingly durable and accurate watches have faithfully accompanied their owners on many dangerous reconnaissance and behind-the-line operations conducted in the hot and steamy jungles of Vietnam
Here is a recompilation of information about them.
Within the Benrus Type I versions we can find the Sterile variant and the Type I Class A, while within the Benrus Type II we can find the Type II Class A and Type II Class B.
So, you have 4 versions of these awesome Benrus. The most desirable is the Sterile version, due to its rarity among the others variants.
Firstly, the Type I Sterile (prototype, probably) and the Type I Class A were made. These highly-reliable Type I Class A watches were so successful that Benrus were contracted to manufacture other versions of the watch, namely Type II Class A and Type II Class B (which differed by having a 12/24 hour numerically indexed dial) to be used by members of the Armed Forces not participating in special operations
Some pics for these four versions, when you can see the differences:
Benrus Type I Sterile
You can see that the only marking is a serial number in the case back. No other markings are to be found anywhere on the watch.
Credit pics: H. Seung.
Benrus Type I Class A.
The same watch that the Sterile version but with some markings in the case back.
This watch was designated Class A, which is essentially the highest classification awarded to military watches.
The writings in the caseback:
MIL-W-50717=the military specification
Type II Class A=Class A due to the fact that the hands and the dial of the watch are luminous. Class B watches doesn´t use luminous material.
Benrus=the watchmaker brand must be writed in the back .
6645 - 22 - 1741=Fed / Nato stock No.
X7951=Maker´s Reference
DAAA25-72-CO656=Military contract code.
APR 1973=Date of delivery
SERIAL NO. / 0732=watch´s serial number asigned the day of delivery.
U.S.=United States Property
Benrus Type II Class A.
Credit pics: Christopher Moy..
Benrus Type II Class B.
Let´s go to an in depth view about the Sterile version Type I.
The sterile version of Benrus Type I is also known as the CIA model as it was issued to CIA maritime units along with NAVY Seals and Green Berets during Vietnam War.
These sterile watches, along with other Benrus dive watches, are non-magnetic to allow the wearer to work with magnetic mines underwater. And the "sterile" differs too, from the more common types I and II, by the fact of not having markings in the case back, only a serial number inscribed on the caseback…other than that, no other markings are to be found anywhere on the watch. Neither the military specification number, nor the issue date.
It is thought by many that the "sterile" watches were issued to covert operators. This lack of identification on the watch would maintain a level of deniability in the event the soldier was captured during a covert operation. Another less exotic (but probably more believable) theory regarding these "sterile" watches is they were unmarked prototypes issued for testing prior to regular production.
Certanlly, I think that we are speaking about unmarked prototypes, which makes them highly desirables.
These Benrus use an one piece case, Promethium PM-147 luminous substance (no Tritium substance), a rotating bezel to friction (no clicks) and a dial that only seeks maximum readability ....
The dial specifications:
Credit pic: BrandonS
In the flesh, these Benrus have an impressive dial, with an awesome readability, and a depth look. In this watch, in fact, less is more.
Many military equipments exhibit signs of well-regarded design philosphy, namely that form follows function. This is no exception to Benrus. The appearance of the dial, as you can see, is heavily borrowed from Rolex Submariner but with essentially no writing whatsoever - not even the manufacturer's logo - making the watch extremely legible, which is what all dive watches should strive for in the first place.
Another point that makes different these watches is the use of Promethium in the indexes. This PM-147 was used too in the Tornek TR-900. It´s quite unusual in the watches of the era, because quite all the diver watches made (Rolex, Omega, Blancpain, etc) used Tritium in these indexes.
Another point to be said is that it seems that there is no luminous marker at 12 o'clock position on the bezel. Well, you've guessed it wrong. The entire inverted triangular mark glows.
The hands have a "stair" configuration, as you can see in this pic…
Credit pic: H. Seung
The crystal is screwed down to the face of the case with an unique metal O-ring gasket. Screw-down crystal and one-piece case design allowed superior water resistance for these Benrus dive watches.
Well, to be sincere, these watches doesn´t have an one-piece case. Commonly referred to as one-piece case, the Type I and II, are in fact two-piece cases. The back is highly pressed so that is permanent. We can access to the movement through the front of the case, removing bezel and crystal. This system requires a two-piece stem, considered by some a weakness of this watch.
One pic is better than words…
These diver watches are true toolwatches, born to be a great company in extreme conditions. Ziggy Wesolowski, author of Concise Guide to Military Timepieces, reports the watch to have been tested to depths of 495 feet.
The black plastic coated bezel is somewhat puzzling since it has 0 to 11 marks instead of the more common 0 to 59 marks found on many dive watches. The graduated minute markers present between 0 to 4 were most likely used for measuring decompression times during dives. Anyway, this unsual bezel design have been carried on to later military watches, namely Adanac and Marathon watches.
The heavy steel case measures 47.5mm lug to lug, 42.4mm across the crown, with thickness reaching 15.3mm. Rigid strap bars are fixed to the case and takes a 20mm black nylon band. It has a screw-down crown with crown protecting shoulders that protrudes smoothly from the lugs. Probably, the most impressive thing in the general appearance of the watch is its true presence in your wrist, its strong look and the finish of the case: a kind of microbille case with an awesome grey finish.
One of the beautiful aspects found on this Benrus dive watch is the perfect dome shaped plastic crystal. It is very thick, about 3mm, and looks extremely tough.
Movement is Benrus signed 17 jewel automatic movement. One of the most unusual things with this movement is the fact that it has hacking seconds. It´s an Eta 2620 modified by Benrus due to the military specifications. It beats at 21,600 bph, and has 42 hours power reserve.
Zodiac Seawolfs of the same era were known to use these movements as well, which kept accurate time if properly maintained and regulated.
Here is a closed pic of the movement…
Hope you enjoyed this recopilation of information searched in the net about this true toolwatches. It has been my pleasure writing and making it…. But my pleasure is really stronger admiring it in my wrist 
I bougth this watch to a collector from Haway and its last owner was an US military watchmaker in Vietnam.
Best to all my dear Purist´s Friends
Emilio.
Credits:
All the info in this post is searched from the net.
1- Thanks to Nicolas who discovered to me this awesome watch and for his info about it here, in the Purist.
2- I have to credit the info and the pics to:
- Scubawatch.org g
- H. Seung page
- posts by Vegaban, in some spanish forums.
- Billy Schorr.
This message has been edited by E.J. on 2010-04-17 16:23:09 This message has been edited by E.J. on 2010-04-17 16:34:53
An in deep view about the Benrus Type I Sterile.
Thanks, Mkvc!
Deep subject
I'm more convinced of the exotic explanation . . .
Both explanations are interesting, and exotics at the same time...
Thanks, MTF..
Plausible deniability ...
Really thanks, Andrew.
informative
Thanks, Faisal. Informative and interesting review...
very informative review thanks Emilio and an excellent example you have
A Class I from 1976.... this is my birth year, Graham.
This watch talks to me very loud, Emilio.
Thanks Hermano. I´m sure that your Autopsy would be perfect!
Great Post!! Nicolas Make me discovers this amazing watchs too. About the "deniability" :
Thanks, Pifpaf.
Sterile?
An excellent post, Emilio!
Daos, Why girls always love Bad Boys?? :)))
Bad boys are the most fun! :-)
Yes, Daos...I´ve just ask to my wife...
very comprehensive review...
Really thanks, Stefan, for your kind words...
Very nice & good article.
Thanks, Andy!
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hi Kimby, in its...
