The Day (New London, CT) on Monday had an intriguing article about DARPA’s Underwater Express. This program aims to prove engineering approaches for a manned minisub able to carry high value cargoes submerged at 100 knots — a “super-fast submerged transport,” or SST. Underwater Express was announced with a request for proposals in 2005. The RFP specified supercavitation, a form of enhanced submerged propulsion exploiting a self-made vacuum cavity or gas envelope between hull and ocean to reduce flow resistance by “60 – 70%.” Supercavitation, such as used in the Soviet-Russian Shkval rocket torpedo, is extremely noisy. Even allowing for a breakthrough in how the gas cavity is created and maintained, the classic power-versus-speed formula makes it highly likely that only a rocket engine could achieve the required 100-knot speed for the SST. Yet the RFP mentioned nothing about silencing the technology demonstrator minisub.

After a competition, General Dynamics Electric Boat was awarded a contract which by completion is expected to total $38 million. The deliverable will be a quarter-scale unmanned version of its winning design, to be demonstrated in the waters off New England in spring 2010. The demo is to include runs at up to 100 knots for 10 minutes, with maneuvers to show that the SST is safe at such speeds. GDEB says they’ve solved the challenges of maintaining a stable gas envelope while accurately controlling the test vessel’s depth, course, angle of attack, and speed. Details are top secret.

I’d been wondering what good there might be to a manned minisub that, unlike a rocket torpedo, has to be reusable and survivable — but which would, whenever moving fast, make a huge passive sonar signature, broadcasting its presence to any enemies for miles around. Besides, what missions would it be used for that couldn’t be done by a HALO insertion and Osprey extraction, or for that matter by a slow moving battery-powered mini like some Improved ASDS? When The Day’s article came out, I decided to ask a source. The rest of this is my interpretation of the answers I got, sprinkled with public info and my own conjectures and commentary.

Underwater Express might for instance be used to extract a SEAL team from a beach, perhaps along with an important defector or prisoner, or maybe with some “confiscated” nuke warhead cores or other nuclear tech, in environments where air control is disputed by cheap but lethal man-portable missiles, but local undersea surveillance is weak due to the local regime’s technical limitations plus coastal environmental noise. Such missions need not be planned for actual wartime. They could be used instead for smash-and-grab police actions against rogue states or terrorists threatening to use WMDs. They might be used to rescue kidnap victims, hostages, or POWs. The key to an SST’s possible utility is that it provides the option to go in and out fast but noisy, rather that quiet but slow.

The tactical advantage of going in and out real fast, underwater, would be the plausible deniability of the whole operation afterward, combined with the rapidity — barely 7 minutes each way — at which the mini and its commandos and passengers/cargoes could dart inshore and away again from the relative sanctuary of international waters beyond the 12-mile limit. (Presumably, the U.S. could attribute any sonar recordings of the SST op, flogged to CNN or Al Jazeera, as “just the usual lava displacements.”) Total surprise, and speed and precision of mission execution, would obviously be essential, but Navy SEALs and other elite special ops folks excel at exactly such traits.

The mini could be quietly dropped off by a full-size nuclear sub that stealthily leaves the area, before the mini starts the mission clock ticking by firing up its main engine(s). It might be picked up right after the mission, quickly and somewhat covertly, via one of the flooded amphibious warfare docks available within a passing surface-ship strike group, with SSN escort, that would certainly provide a powerful 3-D self-defense envelope. This strike group might be deployed to do broad racetracks off the hot-spot coast from the moment when tensions first start to heat up toward a crisis point, keeping the enemy guessing as to what sort of raid(s) might be attempted, where, when. In fact, the strike group might conduct repeated LCAC exercises outside territorial waters, before and after the undersea raid. Rather deafening themselves when zooming along on their air cushions about as fast as a fleeing SST would go, they could lull hostile defenses in advance, and serve as very handy diversions and mobile noisemakers when the time came.

While the noise of a supercavitating SST would make acoustic detection likely, even without LCAC support its corresponding high speed and ability to zig-zag could render the rest of the opposition force’s targeting cycle — localization, identification, tracking, and accurate attack — extremely difficult. With a sustained top speed of 100 knots, the mini could outrun any conventional torpedo; due to its speed and maneuverability, it would be very hard to hit with even a supercavitating anti-submarine weapon. It could be there and gone before the enemy has any chance to start to react, say by launching some helos with active sonobuoys, or vectoring in patrol boats with depth charges.

At least that seems to be the idea. The Day’s piece points out that controllable, maneuverable supercavitation might yield big dividends in more efficient propulsion systems for civilian ocean transportation. Remember, Underwater Express is a proof of technology project only. The current EB contract is not meant to produce an operational SST.

Joe Buff

  • Mat

    Super cavitation seems great for torpedos as they ar harder to defend against than misles ,but i dont se a pint in a 100+kn rocket powered sub taht would transport people.If you are detected and need to move fast air transport or even a fast boat can do it safer not you have time to slowly but quietly get away.
    And lets make it clear for all Stealth fans that stealth planes offer only limited stealth and to gain an edge often utilize huge strike packages of fighters ,Wild Weasel and EW aircraft to operate in any high threat scenario ,thay are very detectable but at reduced ranges so gaps in air coverage can be exploited but not always especialy when the enemy operates lots of mobile SAMs that move around and switch on and of in Serbia campaign US lost at least one probably 2 F117 to a 60

  • irtusk

    i would assume a secondary propulsion system so it could go in quietly and then make a speedy exist

  • Garritt

    Concerned about the impact on sea life; very loud underwater noise has a demonstrable effect on marine wildlife.

  • Mystick

    The only thing I see this being useful for in active mission terms is quickly delivering small strike teams to asymmetric blue water targets, such as a hijacked cruise ship or something of the like without passive sonar.
    Its too fast for littoral use, for several reasons… littoral waters are notorious for sudden obstructions and topography changes… the limited depth would make the passage of the craft quite visible on the surface due to the rapid displacement of water and subsequent wave formed by it.
    ‘Maneuverability’ is a term subject to a plethora of qualifications… a Mach 2 jet fighter is considered ‘maneuverable’, but still takes a mile to execute a 360 turn at high speeds without squashing the pilot or damaging the airframe.
    I’m curious what the navigation sensors on the craft are. They would almost have to involve some form of inertial reference device, since GPS doesn’t really work well underwater, and sonar devices would have problems due to the fact that the sensor would be encased in a bubble of gas, creating an air/water interface(which is what active sonar detects) that would preclude the use of active scans, and flow noise would severely limit passive scans.
    As a proof of concept for civilian transport, fine… let’s see what we can do. Although I think a ground-effect surface craft such as the Russian ‘ekranoplans’ would be faster and more efficient. Especially if the cost of $38 million scales from the quarter-scale prototype currently proposed.

  • flying fart proudly joyned

    i think 10 years swiming with this sub and our oceans will became dead like on the Jupiter.

  • Will

    “Super cavitation seems great for torpedoes as they are harder to defend against than missles”
    The Shkval moves along a pre-determined course, most likely a straight line. As Mystick mentioned, sonar doesn’t work because the torpedo is inside a gas bubble of it’s own making.

  • PolicyWonk

    The notion of having a Virginia drop this thing off and then leaving the area, then an inbound and outbound dash (really loud), seems dubious.
    At the end of the mission, the Virginia would presumably have to return to the area to pick up this vessle and crew for the return home.
    It seems to me that this would provide an alert as to where the mothership is (or soon will be).
    According to Ben Rich’s book, they came up with designs for super stealthy subs that the navy didn’t want because “they don’t build subs that look like that”. Maybe the navy should revisit those designs, and the Sea Shadow concept again.

  • joe buff

    Commentors raise some real good questions about safe littoral navigation of an SST doing 100kts. Two thoughts: A survey of possible routes to and from shore in advance might be needed by stealthier sensor platforms. This could allow a pre-programmed autopilot system to control the SST on its trajectory (I’m right now more comfortable calling it that than “its course”). Remember the Virginias have an extremely capable cruise-by-wire ship control autopilot said to be able to maintain depth (below the surface) at the bow and stern to within 0.1 feet. Presumably this approach could also be used to maintain depth (“bottom clearance”) below the keel very precisely, and hopefully do so well enough at very high speed. Also, the open media re supercavitating weapons in recent years has discussed torpedoes with a nose that tapers to a flat tip which actually rides in front of the gas envelope. This tip thus maintains contact with the water and could (supposedly in some designs actually does) include guidance and navigational sonars. Still, there are some daunting and yet exciting engineering challengers; it would be great if they can be solved practically, soon. Well, GDEB spokespeople said in The Day’s article that some of these problems have already been solved. Details are, alas for all of us curious about such defense-related hi tech things, classified top secret.

  • renomd

    If you want speed without the acoustical signature, why not use a ground-effect vehicle? Moves up to 300 mph, no contact with the water, larger payload (think vehicle size), longer range, and could probably incorporate stealth design features. This sounds like somebody has $38 million just burning a hole in their pocket.

  • Byron Skinner

    Good Morning Joe,
    I’ve learned not to pass judgement on DARPA projects before they mature. Very often what seems to be dumb a** idea such as this turns out to be something very useful. At $38 million which, which is pi** water money for the DoD it’s worth a look at.
    Byron Skinner

  • Valcan

    i think 10 years swiming with this sub and our oceans will became dead like on the Jupiter.
    Posted by: flying fart proudly joyned at July 29, 2009 11:45 AM
    Do i have to explain how wrong that comment is lol

  • demophilus

    Maybe you could use the noise as a surrogate for other active sonar emitter systems?

  • WJS

    Just a thought. If it goes 100 knots, is manueverable, and has stamina fuel wise who cares how noisy it is. If nothing in the water can catch it what does it matter? Comment?

  • joe buff

    WJS: Yes I think you hit squarely on the basic idea of Underwater Express. So long as you don’t crash into an old wreck or a sandbar, 100 knots underwater is a great way to “get out of Dodge.”

  • Ptsfp

    All right Joe, who are you trying to kid? According to your last article, “UFO IN OUR BAFFLES, COMRADE CAPTAIN!” the Reds already think we have something that does 230 kts…
    We also have the cool underwater thingies that can fly too. I think Darpa is just blowing smoke. :)

  • DualityOfMan

    This program seems a bit silly to me. The whole point of submarines is basically stealth. In the Cold War, this was so our submarines could tail Russian submarines. Now it has to do with keeping power projection secret and/or stealthy.
    If we’re going to study supercavitation, torpedoes seem to be a better choice. If we want minisubs, stealth is probably better. Accelerating to 100 kts underwater is like holding up a giant “look at me, I just infiltrated your coastal waters” sign. If they can’t see you, who cares how fast you get out?
    $38 mil is pocket change in the budget anyhow. I think it’s good that DARPA provides pretty inexpensive development of radical technologies for future use.

  • Tom

    So what if it is noisy as long as the mission is properly planned to beat the enemy capability to respond!
    Even among nations that do have robust maritime defenses and/or paranoid leadership, there are very few situations where an enemy could react quickly enough to catch or kill something moving 100 kts underwater.
    The greatest potential drawback is that IF this system was used to enter the enemy location it might raise an alert that would interfere with any sort of clandestine mission. Of course, as someone else already noted, there is no reason why an OPERATIONAL version could not be fitted with dual propelsion systems to provide a low-noise entry combined with a fast exit.
    Keep in mind that this is a DARPA research project, not an operational procurement. Although DARPA projects frequently do turn into operational hardware sooner than outsiders might expect, the bottom line is that most DARPA projects are research to address a single specific problem or closely related set of problems. DARPA is not designing a Seal Delivery Vehicle – they are working on technologies for fast underwater transport. What someone later does with that technology and especially how this technology is merged with other technologies is outside the scope of this project.
    If this technology works out, I would bet that in a few years we will see a stealth sub with a 100kt dash speed capability.

  • joe buff

    Tom et. al.: You give a very good summary of what DARPA is and isn’t trying to accomplish with the Underwater Express project w. GDEB. While the article in THE DAY didn’t mention dual mode (high-speed rocket/low-speed batteries) propulsion, it did describe the GDEB design as 8 feet in diameter (beam) and 100 feet length. Notionally, this is like a 60ish-foot ASDS with a 40-foot supercavitating back-end. The ASDS had a battery-powered screw that could make 8 knots for 125 miles. The concept of the ASDS was stealthy ingress and egress. (The project was canceled because the actual test article was too noisy and vibration-prone, and had a bad fire during a battery recharge.)
    Thus, an SST could be thought of, and used, as an “ASDS-Plus.” It could offer the option for a stealthy minisub ingress and egress — with another option for an “emergency exit” if the commando team during its mission on land were compromised, or the mission as planned involved having to “make a datum” that revealed the team’s presence to opposition forces. (In that case the loud egress signature does not further compromise the mission.) The fast/loud egress option could then be invaluable to team survivability. The utility of that emergency exit capability would be even greater if the mission parameters specified as vital to success the assured retrieval from hostile territory of some high-value personnel and cargo.
    Make sense?

  • gsak

    We need this for clearing datum after an SLBM launch, to avoid counter-battery fire. Assuming we work smaller solid propellant motors into a Virginia-sized hull.
    Additionally, this could be useful for fast transit from the 100-fathom curve to the area of operations.

  • M167A1

    I wonder at the manned requirement too.
    Would make a heck or a torpedo and it might be a good way to project mines into a harbor if you don’t mind the other sid knowing you did it.
    It might be a very rapid type SDV. Get a seal team ashore asoon as possible for a raid, they jump out raid the brewery or whatever they are there for and dash off while ther other side is wondering why the waterfront is burning..
    Small change and a perhaps useful tech. Lets do it.

  • Jean

    The wildlife argument is quite interesting, especially when turned the other way around. What would happen to a manned sub hitting a whale, a great white shark, a whale shark, a manta ray or a big tuna at 100kts? I know such moderate risks are part of the business for the military but so far as considering this an acceptable mean of civilian transport, I guess i’d still prefer, and by far, flying a respectable 500kts at FL390, even if I’d be scared to death of flying, than blindly cruise this “slow” into what I can’t see nor detect, if I understood you guys correctly.
    But OTOH, since every sides have better and better listening devices to detect the ennemy, this does sound (no pun intended) to me like an excellent way of “scrambling” those listening means and hide one’s own subs moving onto a target. They may not even have to be near the attacking sub (or a spying one) if they’re so noisy and could be cruised routinely anywhere to hide the “real moves”. Does it “sound” like military strategy now?

  • Oblat

    Seems a lot of trouble to go to when a zodiac loaded with a marching band playing at full volume would be just as effective.
    But it is hilarious after the years of poo-pooing Russian and Iranian supercavitating torpedoes as being too noisy only to see the same people comment that the same technology used for stealthy seal mini-subs would be cool. Talk about snake oil customers.
    If ever there was a project that held up both hands to be canceled this would be it.

  • John

    Sounds good. Now all they have to do is spend $18 billion dollars on it, build 3 and cancel the program.
    Then it will be a *real* US military program.