Unmanned Underwater Vehicle (XLUUV) CONOPS

The Navy is embarking on a program to acquire dozens/hundreds of unmanned underwater vehicles (UUV) with [** warning: shocking news ahead! **] no concept of operations (CONOPS) to guide the design.  Okay, that was probably the least shocking news you could have read, right?  I mean, the Navy hasn’t developed a CONOPS for anything other than admiralty promotions in many decades so why would this be any different?  We’ve seen from the LCS program what happens when you commit to a full production program with no CONOPS and no prototype.  Way to learn a lesson, Navy.

 

Since the Navy won’t develop a CONOPS, let’s see what, if anything, we can come up with, along those lines, for a UUV.

 

The Navy is developing dozens of different UUV designs in many different sizes.  Most are just glorified torpedoes.  We’ll ignore those as the minor pieces of equipment that they are.  Instead, we’ll focus on the largest UUV, the extra large unmanned underwater vehicle (XLUUV, also called Orca).

 

… the Navy defines XLUUVs as UUVs with a diameter of more than 84 inches, meaning that XLUUVs are to be too large to be launched from a manned Navy submarine.  Consequently, XLUUVs instead will transported to a forward operating port and then launched from pier. The Department of the Navy’s March 16, 2021, unmanned campaign framework document states that the XLUUV will be designed “to accommodate a variety of large payloads….”  The Navy testified on March 18, 2021, that mines will be the initial payload for XLUUVs.  More specifically, the Navy wants to use XLUUVs to, among other things, covertly deploy the Hammerhead mine, a planned mine that would be tethered to the seabed and armed with an antisubmarine torpedo, broadly similar to the Navy’s Cold War-era CAPTOR (encapsulated torpedo) mine.[1]

 

The XLUUV will be based on the Boeing Echo Voyager with some Navy-specific modifications.  That being the case, let’s take a look at the Echo Voyager.

 

Echo Voyager is roughly the size of a subway car—it is 51 feet long and has a rectangular cross section of 8.5 feet by 8.5 feet, a weight in the air of 50 tons, and a range of up to 6,500 nautical miles. It can accommodate a modular payload section up to 34 feet in length, increasing its length to as much as 85 feet. A 34-foot modular payload section provides about 2,000 cubic feet of internal payload volume; a shorter (14-foot) section provides about 900 cubic feet.[1]

 

Boeing Echo Voyager

Echo Voyager has a maximum speed of 7.8 kts [2] and uses a combination diesel-electric propulsion/power system.  On battery, the vessel has a range of 150 miles at 2.6 kts whereupon it must surface and recharge its batteries using its diesel generator. 

 

With a single fuel module in its payload bay, Boeing claims the range is 6,500 miles.[2]  I’ve found no information about the size of the fuel module.  The statement that fuel modules are stored in the payload bay is important because that means that the effective payload space is less than the stated specification of 2,000 cu.ft.

 

The vessel has an obstacle avoidance sonar and inertial guidance.

 

The maximum dive depth is 11,000 ft.[2]

 

In 2019, the Navy contracted with Boeing to produce four XLUUVs for $43M which is just under $11M apiece.[2]  The contract was later expanded to include a fifth vessel.  Funding will come from a Navy Research and Development account similar to the funding mechanism used for the first two LCS.[1]

 

The preceding description suggests certain operational characteristics that will influence the CONOPS and selection of appropriate missions.

 

 

CONOPS Characteristics

 

Speed – As noted, the vessel is very slow.  The maximum speed is 7.8 kts and, presumably, the economical cruising speed is much less.  Given the statement about the range on battery being 150 miles at 2.6 kts, this suggests that the cruising speed is 2-3 kts.  This has a major impact on operations.  For example, pier launch and lack of forward bases means that for Chinese theater operations the nearest launch point (disregarding Japan which is not a guaranteed base of combat operations), Guam, would be around 2100 miles from the South China Sea.  Even at the maximum speed of 7.8 kts, the transit time to the South China Sea would be around ten days and a more economical cruising speed of, say, 3 kts, would result in around a thirty day transition time.

 

Payload – This is a small vessel with a correspondingly small usable payload.  Consider the Navy’s main postulated mission:  laying Hammerhead mines.  How many mines could fit in a 2000 cu.ft. payload space?  I can’t find any specs on the Hammerhead capsule size, however, there is a picture of the Hammerhead package so a reasonable estimate of the package size is possible.  Knowing the Mk54 torpedo size, we can visually estimate the overall package size.  Assuming the package is sized to fit a 21” torpedo tube, this gives us approximate dimensions of 21” x 21” x 19 ft, for a total of 58 cu.ft.  Simple arithmetic tells us that the maximum number of mines that could be carried in the 2000 cu.ft. payload space would be 34.  However, there needs to be room to move and secure the mines during loading.  It would be reasonable to assume that half the payload space would be dedicated to movement and securing the mines which would reduce the capacity to 17 mines.  Some sort of mine handling and ejection mechanism is required and that would further reduce the number of mines.  If the fuel module is also stored in the main payload section, the number of mines is even smaller.  A reasonable estimate would be a mine capacity of around 12.  See, ref [3] for an interesting discussion of this.

 

Hammerhead Mine Capsule

Range – On the face of it, the claimed range of 6,500 is excellent and suggests that not only can the vessel reach its operating area and return (4200 miles round trip from Guam to the South China Sea) but it will have enough excess range to effectively operate for an extended period within the operating area.  However, as noted, the submerged range is only 150 miles on a single battery charge.  Thus, in order to achieve the claimed range of 6,500 miles, the vessel will have to surface frequently … a very bad requirement for a submarine operating in enemy waters!

 

Communications – I’ve found no mention of communications in any description of the vessel which implies that once launched, the XLUUV will be largely autonomous.  Aside from being very dubious about the success of a truly autonomous vessel for any length of time, this suggests that the vessel’s usefulness in the surveillance role will be limited as that would require frequent and lengthy transmissions from the UUV back to its port - communications that would quickly pinpoint the vessel’s location for the enemy and given the UUV’s very slow speed, it would be quickly destroyed.

 

 

Concept of Operations (CONOPS)

 

In attempting to assemble a CONOPS, what do we have to work with?  We have a small vessel with a small payload (small on the scale of contributing to a war effort).  The vessel, itself, is very slow and unresponsive.  As with any submerged vessel, communications will be difficult once a mission is started. 

 

So, what does that suggest for a CONOPS?

 

It suggests that the only viable missions are those that are very slow developing and can afford to wait for very long periods of time and can be effective with very small payloads.

 

While various articles have postulated virtually every mission ever conceived in the history of warfare, there are only two viable missions that meet the criteria and constraints described above:

 

Mine Laying – An XLUUV can be effective as a mine layer but with a significant caveat: it is only useful and effective for a very small area.  Typically, mines are deployed in the thousands to tens of thousands for a single field.  The very small payload of the XLUUV precludes using it to lay a large field no matter how many XLUUVs we acquire.  That only leaves point mining of a very small area such as a channel or entrance to a harbor or a narrow passage between islands.  For example, one could imagine productively mining the entrance/exit to a Chinese naval port.

 

Surveillance – Given the combination of limited sensors, limited field of view, very slow speed (inability to follow a target), and communication issues, the only type of surveillance mission that would make sense is monitoring a very small, restricted area as described in the mine laying section.  In such a scenario, the XLUUV becomes, essentially, a static sensor and targets come to it (or not – that’s useful information, too).  The caution is that any important and restricted area will be heavily patrolled by the enemy.  Whether the craft is quiet enough to escape close scrutiny is unknown.  It will have to be extremely quiet since it will have no ability to fight back or maneuver to avoid detection.  Further, the extremely limited battery life that requires frequent surfacing to recharge is a major liability in this mission.  Without knowing exactly how stealthy the XLUUV can be (factoring in frequent surfacing for recharging), surveillance is a pretty iffy mission.

 

 

Rationale

 

Given the lack of worthwhile missions, why is the Navy so enthusiastic about building these UUVs?  What is their rationale?  Cheapness, compared to a real submarine, is obviously a major factor and if the XLUUV had even a fraction of a real sub’s capability, this might make sense … but it does not. 

 

Does the Navy really view these as a cheap replacement for real subs?  That would be hard to believe but we’re replacing Burkes with small, defenseless, unmanned surface vessels so … maybe.  Could they, in some twisted way, view them as a cheap, indirect replacement for surface ships in the overall force structure? 

 

Is it technology for its own sake? 

 

Is it sheer, unmitigated stupidity?

 

A handful for the limited mine laying mission is reasonable but any more than that cannot be justified and yet the Navy seems committed to a large production run and making these a significant portion of the future fleet structure.  It’s baffling.

 

 

Conclusion

 

It is very difficult to postulate a worthwhile concept of operations other than the very limited mine laying mission described above, although that single mission does have some value.  That does not, however, seem to justify the acquisition of more than a handful of XLUUVs – certainly not the large program the Navy seems to want to pursue.

 

Acquisition of this XLUUV will require a supply/support logistics train, administration, operators, specialized equipment, specialized maintenance, etc.  Does the limited scope of useful missions justify all this?  I’m doubtful.

 

This seems to be yet another case of the Navy jumping on the unmanned technology bandwagon for no demonstrable good reason;  technology for the sake of technology.

 

This also continues the trend of minimizing the value of raw firepower in combat, as the XLUUV offers no significant firepower.

 

At best, this is a niche mission/craft with a significant cost in terms of acquisition and support.

 

 

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[1]Congressional Research Service, “Navy Large Unmanned Surface and Undersea Vehicles: Background and Issues for Congress”, 19-Jan-2022

 

[2]https://www.thedrive.com/the-war-zone/26513/boeing-is-building-the-navy-big-orca-submarine-drones-to-hunt-and-lay-mines-and-more#:~:text=Boeing%20experimental%20Echo%20Voyager.%20The%20diesel-electric%20Echo%20Voyager,and%20use%20its%20air-breathing%20diesel%20generator%20to%20recharge.

 

[3]Strikepod Systems website, 1-Jun-2021,

https://www.strikepod.com/xluuv-offensive-mining/#:~:text=Little%20is%20known%20of%20the%20CDM%2C%20but%20it,very%20shallow%20water%2C%20or%20possibly%20the%20surf%20zone.