The First in a Series
This will be the first in a series of posts about strike systems. In modern warfare, with ubiquitous ISR—Intelligence Surveillance Reconnaissance—no assets can move freely on the surface. All manner of strike systems with sophisticated guidance can attack them with great precision. Examples include artillery (e.g., GPS-guided Excalibur shells), JDAMs and other glide bombs covered in earlier posts, cruise missiles, and ballistic missiles.
A great deal is made about the accuracy of these systems. Before launching into further posts, I thought it would be a good idea to celebrate our inner nerds and clarify objective metrics of accuracy. Why? There’s a lot of confusion out there.
Consider two simple but different statements about the Kalibr cruise missile:
- “The Kalibr has an accuracy of 2 to 3 meters.”
- “Baloney, the Kalibr has an accuracy of 50 meters.”
Which one is correct, and what exactly does this mean?
Both statements can be correct. Accuracy depends upon the metric and guidance system employed. The first statement is correct for the Russian military version of Kalibr, which employs GLONASS guidance. GLONASS is the Russian version of our GPS. The second statement is correct for export versions of Kalibr, which are not equipped with GLONASS guidance.
Different Methods, Different Characteristics
There are different guidance methods, with different accuracy characteristics. Examples include GPS/GLONASS, inertial guidance, laser-guided, terrain-following, radar-guided, optically guided (remotely by a human controller), wire-guided, and on and on. The guidance technology that can be employed is bewildering, and sparks counter-technology developed to defeat it. Electronic Warfare Systems are defeating a high percentage of precision strike systems. We don’t hear about Excalibur rounds in Ukraine anymore because EWS has drastically reduced their effectiveness.
How is accuracy measured? It is a probabilistic concept. The simplest metric is the Circular Error Probable (CEP). How is this defined?
Circular Error Probable:
“The radius of a circle, centered on the aiming point, within which 50% of strikes will occur.”
Related: “93.7% of strikes will occur within a circle of twice the radius of the CEP.”
So, in the case of the GLONASS-guided Kalibr, 93.7% of strikes will occur within a circle with a 6-meter radius (12 meters across). This is how to visualize CEP:
These are simple models based on a normally distributed guidance technology. In practice, technologies will not be perfectly normally distributed. For example, artillery, or even the “beaten zone” of plunging machine gun fire, will fall in an elliptical pattern about the long axis of the gun, not a circle. Arguably, the same will be true of ICBM missile strikes. But it is useful to keep things simple as a starting point for comparison. So, we get the concept.
So an interpretation of CEP would be to make a statement like “A Kalibr cruise missile, equipped with GLONASS, will strike within 3 meters of its aiming point half the time.”
If you want to be confident of putting one in a 3-meter radius pickle barrel, you need to fire at least two Kalibrs.
Only Correct on Average
One also needs to realize these statements are only correct on average—the larger the number of strikes you make, the more likely it is for the metric to hold true. If you are given a CEP of 3 meters, fire two Kalibrs, and find that both fall outside the circle with a 3-meter radius, that doesn’t make the CEP wrong. This is very important to understand. The metric is true over a large number of strikes, say n>30 or more. If you fire 30 Kalibrs, you’ll likely find 15 strike within the CEP circle. Or maybe you get 14 in, or maybe you get 17 in. It is a probabilistic concept, true over many trials.
This video discusses the accuracy of the M777 howitzer and the Excalibur shell:
The math gets more and more complicated. Let’s say you’re attacking an aircraft carrier ringed with layered Aegis missiles defense and CIWS. There are complex formulas to determine how many anti-ship missiles you need to salvo in order to defeat the carrier’s defense screen.
In summary, the accuracy of a weapons system depends, among other things, on its guidance. It can be summarized in a metric called the Circular Error Probable (CEP). This is the radius of a circle within which, on average, half of a large number of strikes will land. While the topic of accuracy is much more complex, this brief discussion gives us the background to appreciate statements made about different systems.
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By Cameron Curtis
Cameron Curtis has spent thirty years on trade floors as a trader and risk manager. He was on the trade floor when Saddam’s tanks rolled into Kuwait, when the air wars opened over Baghdad and Belgrade, and when the financial crisis swallowed the world. Having written fiction as a child, he is the author of the Breed action thriller series, available on Amazon.
Editor’s Note: All of us here at SOFREP are big Cameron Curtis fans. Be sure to check out his Breed series of thrillers. Once you pick one up, you won’t want to put it back down. — GDM
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