Jeffrey LewisSecret Screws

Oh, you thought this was a Larry Craig post. You are going to be very disappointed.

Or maybe not. This is yet another post about our favorite form of smut here at Arms Control Wonk — wonkporn.

See that picture above? Notice that instead of a tasteful tarpaulin, leaving something to the imagination, the propeller — which the Navy calls a “screw” — is exposed, naked as the day it was installed, for all to see?

The image, a rare glimpse of an Ohio-class submarine’s secret propeller design, is from Microsoft’s Virtual Earth. Dan Twohig found the image and linked to it on his blog, Monster Maritime, setting off a round of consternation and grandstanding not seen since Henry Miller published Tropic of Cancer.

The Navy Times refused to publish the picture or link to Twohig’s website. (Twohig’s blog, by the way, is still the best place to follow the story.)

The Seattle Times was not so coy, linking to both Twohig’s website and an amazing article on the Smithsonian website by Paul Forsythe Johnston, called “The Taming of the Screw.”

Johnston, Curator of Maritime History at the National Museum of American History, details his efforts to have a submarine propeller included in a Smithsonian expedition. During his efforts — which resulted in the inclusion of a Sturgeon-class propeller model in the exhibit, “FAST ATTACKS AND BOOMERS: Submarines in the Cold War” — Johnston also uncovered an enormous amount of information about propeller design that was available, including a very similar picture of a 1970s vintage screw (right) available since the early 1990s.

Norman Friedman published this image, showing the stern of a Los Angeles-class (SSN 688) submarine at Holy Loch, Scotland.


  1. Lao Tao Ren (History)

    The irony is when this stuff finally ‘leaked’, it was not a small, but a grand hemorrhage.

    All secrets leak out over time, but talking about a flood.

    Not only is the shape of the prop leaked (which allows any competent 2nd tier power to reconstruct it theoretically), but also other interesting technical details like the need for interior structural reinforcements (leaked by a person who asked the navy for permission to cut a donated prop and was refused, then turned around and posted the refusal on the web), and such things as how to blend the prop with the rest of the hull.

    There is, of course, still the need for good reverse engineering, hydrodynamic analysis, simulations, and rather sophisticated machine tools to make this, but there are ways to get around that issue too.

    Not good.

    Careless navy personnel and contractors is worth many spies.

    Thank heavens the US face no obvious enemy who is motivated and determined to challenge the US at this time.

    Fortunately, rapid progress in computing power, sensors, networking, and software that diminishes the advantage that gee whiz devices like these props once provided.

  2. Nate Hughes (History)

    I can’t recall now, and I certainly can’t find it on the Navy Times website, but when the Navy Times initially published the Monster Maritime story, it was earlier than Aug. 10 and unless I’ve totally mixed this up, I do recall getting to from that Navy Times article.

    Wonkporn…I like it.


  3. Carl (History)

    If something like propeller design is still consider such a secret, why aren’t the dry docks covered? Why isn’t access to the dock heavily restricted and things like cell phones with cameras confiscated? It seems to me that a satellite or a random photography plane passing overhead would be the least of the Navy’s worries in information like this getting out to 2nd tier powers who otherwise wouldn’t have ways to acquire such data.

    Does anyone know if this design is still revolutionary to the point where submarine producing countries, for example China, haven’t already come up with something similar on their own?

  4. Pete (History)

    no shroud, no compromise.

    much ado about nut’n

  5. Pat Flannery (History)

    This isn’t the end of the world as far as propeller design secrets go, the design concepts of our propellers were sold to the Soviets in the 1980s by David Walker, who was later arrested for espionage.
    The same sort of propeller design shown in the photo is being used on many countries submarines nowadays, and without the details of what the precise thickness and profile of the blade along its entire length is, this photo is pretty much worthless as far as giving away classified information.
    Even if you had that data, you need a very precise giant milling machine to manufacture such a propeller.
    The Soviets had to buy one from Japan, as their own industry wasn’t up to building something of that complexity.
    Besides that, third world nations buy submarines from outside sources (Russia and Germany being two favorite sources of supply), they don’t design and build their own.
    So once Russia got the secret screw design, the cat was out of the bag as far as any third world threat from secret subs.
    Why build it when you can buy it?
    The whole thing is a tempest in a teapot created by the military as another step in a continuing campaign to try and censor the internet’s content, Chinese-style.
    It got started with the soldier’s blogs from Iraq, it continues here.

  6. Harry (History)

    What’s revolutionary about this design is the slightly extremer (if that’s a word) sickle shape to each propellor, it’s giganitic size, which gives way to more props all around.

    So in the end – it’s bigger, better, and more refined dynamically speaking.

  7. Lao Tao Ren (History)

    The picture did give away secrets. No, it is no longer that secret. But:

    It is known that in following generations, the screw is enclosed in a duct rather than being ‘open’.

    Thus, a detailed examination of this and similar photos will give a very good clue as to the design limits of skewback props in a large, ocean going sub application.

    What the picture showed is the diameter of the prop, the degree of skewness, a good view of th shape and size of the blades, and how it all blends into the sub —- enough to start cranking out simulations.

    Working backward to how much power is needed to push a boat of that mass and shape at x speed / rpm with what noise envelope, and instead of solving a problem from scratch, you are solving a problem knowing the answer exist in the back of the book —- a much easier task.

    Any first rate power (US, UK, Germany, Russia, China) is capable of doing the basic theoretical work and the back engineering (and have the equipment and other expertise) to get a workable screw that may not be as refined as the best of the US screws.

    However, the ducted designs —- that is still pretty closely guarded.

    Knowing the limitations of the classic skewback would be a great step forward to the next technology.

  8. Pat Flannery (History)

    Even the ducted props such as used on the Seawolf and Virginia classes aren’t really all that new. The Typhoon class used ducted props:
    (in fact they go a lot further back than that in Russian service – even the elderly Romeo class had short ducts around its props, though these were probably to protect the props from damage more than for silencing or higher power output). At least in the case of the ducted props, photography will not be as easy as the case shown here; you’d have to take an image from the front or back of the duct to see exactly what was inside of it, so overhead photography won’t show much.
    The Ohio prop looks very much like an enlarged Los Angeles class one, which isn’t surprising since they come from the same time period as far as design goes… and as the article points out, the design of the Los Angeles class prop has been known since the early 1990’s and “The Taming Of The Screw” article.

  9. Pickled Eel

    Pat Flannery is on the money – this technology was compromised twenty years ago or more by the milling and lathe technologies being sold out of Japan. It was a little worse than Pat paints it but the end result was the same.
    And let’s face it what sort of metrics are you going to glean from a photo of this resolution. Very little, if anything.

  10. Polymath (History)

    Does the perspective of the propeller image look a little funny to anyone else?

    The propeller looks to me like it is tilted at a different angle from the vertical walls of the dock.

    Maybe they’ve put a dummny propeller over the real one?

  11. Lao Tao Ren (History)

    I just tried the link in the blog post and it no longer works —- apparently someone has seen fit to take down the formerly very clear picture of the SSBN screw.

    Could it be that the Navy Brass has spoken?

    Maybe it did reveal a bit too much for the image to be left ‘in place’?

    I hope some contractor / navy personnel get what should be coming to them.

    Negligence is not cool.

  12. Lao Tao Ren (History)


    Please scratch that last comment, there was a problem with your link. I got it to come up here:

  13. Pat Flannery (History)

    I knew I had seen a color close-up photograph of a scimitar bladed sub prop like that before in one of my books, so went searching for it.
    …and I found it on page 37 of “Modern Naval Combat” from 1986, showing the screw of a Italian “Nazario Sauro” class sub.
    The photo shows a seven-bladed prop nearly identical to the one shown in the terrible photo of the Ohio class sub in drydock, and on the stern of the Los Angeles class attack sub.
    BTW, that photo of the LA class prop is reproduced on page 163 of “US Submarines Since 1945” published by The Naval Institute Press back in 1994.
    They don’t exactly have a reputation as traitors.

  14. j house (History)

    What is most intriguing is the ability of the average joe to pour through satellite imagery in their pajamas looking for intel like this.Imagine the day when we get public access near real-time 1 meter resolution. We will have moved closer to a time when governments cannot lie about the movements of their armed forces prior to an attack

  15. j house (History)

    The size of the prop and other geometric data can easily be gleaned from the image…anyway, the DOD already knows much of the design spec is compromised, so they don’t care about a visual from above, especially at this resolution