Scout Ship

We recently discussed the Navy’s ill-conceived plan to use unmanned vessels as sensor scouts out in front of a surface group (see, “Navy’s Manned-Unmanned Fleet Concept”).  We noted problems such as small size, limited endurance, questionable speed, high cost for an expendable vessel, broadcasting their own location (due to active sensors), and lack of defense.  The alternate option is to use small UAVs which would accomplish all the same goals at a fraction of the cost.

The Navy is correct in their desire for long range sensing – just wrong about how to accomplish it.  As we begin to procure some longer range missiles (LRASM, NSM, anti-ship Tomahawk), longer range targeting becomes critical.  As I’ve said many times, it’s pointless to have a ten thousand mile missile when your sensor is only good to the horizon.  So, good for the Navy for recognizing the need but they missed the mark on how to do it.

In addition to UAVs, there is another option for long range sensing that is actually closely related to the Navy’s unmanned sensor vessel yet solves most of the small sensor vessel’s drawbacks.  The option is a  larger, manned, scout ship sensor vessel but with a different concept of operations (CONOPS).  Let’s take a closer look.

The biggest problem (that’s actually debatable because the vessel has a lot of problems and they’re all pretty major!) with the Navy’s planned 130 ft long sensor vessel is that it will have to use active radar to find anything and get a targeting location.  Think about it … a tiny vessel will have a very low radar mounting.  A vessel that size will have its radar mounted perhaps 20-30 ft above the surface.  That makes for a very short radar horizon – something on the order of 12 nm or so (there are radar horizon calculators readily available on the Internet if you care to play with the numbers).  Using active radar will give away the sensor vessel’s location long before it can find a target.  Plus, with a sensor field of view that small, the vessels will be nearly useless for providing area coverage unless there are a LOT of them and large numbers simply compound the problems we’ve already identified.

The alternative is to use passive sensors.  The problem with this approach is that passive sensors generally provide a bearing but not range.  Of course, the passive sensor can, over time, develop a range by moving and triangulating – this is what a submarine does.  Alternatively, two or more sensors operating at different locations can work together to fairly quickly establish the target’s position.  The problems with small vessels remain, however.  They are poor sea keepers, have limited endurance, and are too expensive to be the expendable asset they would need to be when used the way the Navy intends.

Alternatively, let’s consider a significantly larger, corvette-size vessel that operates not in front of a surface group but around the periphery, offset well to the sides, and uses only passive sensors.  Due to the nature of the various signals of interest and the effects of atmospheric phenomenon (ducting and the like), passive signal detection can occur far beyond the horizon.  Thus, passive detection range is much greater than active sensors.  The trade off, as we noted, is that passive detection provides only a bearing, not range.  This is where using two or three vessels comes in – they can combine their data and triangulate.  The vessels would be offset hundreds of miles to the sides of the area of interest rather than grouped directly in front of the surface group.  Given the much greater range of detection and area of coverage, only a few vessels are required rather than the Navy’s vision of mini-fleets of sensor vessels.

Wait … communicate and triangulate?  How can they communicate?  Haven’t I repeatedly stated that we won’t be able to maintain a viable network of data in peer war, electromagnetically challenged environment?  Yes, I have.  The difference is that this approach does not require constant communication because there is no need for real time data fusion – thus, no network.  Occasional bursts of minimal data are sufficient.  If a burst doesn’t get through, you try again – no harm done.  Further, this requires only minimal data:  conceptually, the sensor ship’s location and the threat bearing it detected.  The smaller and shorter a signal transmission is, the easier it is to get through any interference.  The point of these vessels is not to establish real time targeting data with constant transmissions but to develop situational awareness of a broad area – though we’ll gladly take a targeting quality datum if we can get it.  With broad situational awareness, we can then allocate additional sensors (the UAVs we mentioned earlier or an F-35 or whatever) to the known threat locations and establish the final targeting data – or, we can avoid the area if we want to stay hidden.

Visby Scout Ship

We see, then, that with this approach we can establish broad area situational awareness with just a few vessels that won’t give themselves away and won’t have a negative impact on the surface group’s movement, speed, or endurance and, being far away from the likely area of action, the vessels won’t be at exceptionally high risk and will be capable of limited self-defense, if needed.

What kind of ship fits this requirement?  The Visby would be a good starting point (see, “Ship Stealth and Visby”).  It is corvette size but with adequate sea keeping and the potential for good endurance and range.  It is very stealthy and has the basis for SeaRAM/CIWS self-defense.  Most importantly, it has the size to accommodate all the signals analysis sensors, computers, and analysts that are needed.  In short, it would be a very capable, very survivable vessel for the role.

USS Palm Beach (AGER-3) - Electronics and Signal Intelligence Ship

Repackage in a Visby-Type Hull

A Visby-type scout ship could also be equipped with acoustic sensors (towed array optimized for long distance, passive, convergence zone detection) which would further enhance the usefulness of the vessel.

The ES-3A Shadow (S-3 Viking variant) once performed this signals intercept and analysis role for carrier groups but that incredibly powerful and valuable aircraft was retired without replacement.  In addition, it could only operate from carriers whereas this scout ship can operate anywhere.

This CONOPS offers the advantage of providing detection without the enemy realizing they’ve been detected.  The Navy’s proposed small sensor vessels, using active radar, would be easily tracked and offer no advantage of surprise.

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Note that this is not a case of mutually exclusive, one-or-the-other options.  I’m not looking to replace every sensor platform the Navy has with just this one scout ship.  This is just another option that better accomplishes the Navy’s intent and complements the other sensor options.  What I’m saying is that I don’t want to hear any comments debating one-over-the-other scenarios because that’s not what’s being proposed.

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